Instead of trying to run coverity builds during the regular PR process,
run them during a regularly scheduled cron process.  These only need to
run nightly, so it makes sense to bring them out of the PR process.

(cherry picked from commit 6b92368c)

(cherry picked from commit 24d17562)

(cherry picked from commit 24b8dd82)

(cherry picked from commit 465f8b51)

(cherry picked from commit f7bb4ff8)

(cherry picked from commit 6fb63c92)

(cherry picked from commit dc6e80e2)

The leaks process is not good about handling children.  Ensure that its
child is `nohup`ed so that the grandparent shell won't wait for it to
exit.

(cherry picked from commit 6eb97b6b)

(cherry picked from commit 230eeda8)

(cherry picked from commit b00672b9)

(cherry picked from commit afecd15c)

(cherry picked from commit 7f12c123)

On Linux (where we run valgrind) allocate a smaller buffer, but still an
insanely large size.  This will cause malloc to fail but will not cause
valgrind to report a likely error with a negative-sized malloc.

Keep the original buffer size on non-Linux platforms: this is
well-tested on them and changing it may be problematic.  On macOS, for
example, using the new size causes `malloc` to print a warning to
stderr.

(cherry picked from commit 219512e7)

(cherry picked from commit 6d6700d2)

(cherry picked from commit 67f5304f)

(cherry picked from commit 9e588060)

Script to set up dependencies on a macOS build system.

(cherry picked from commit 87342404)

Sets up a linux host to prepare for a build.

(cherry picked from commit 5bb2087b)

Refactor citest.sh to enable local testing by developers.

(cherry picked from commit 451b0017)

(cherry picked from commit bf418f09)

Add citest.ps1 PowerShell script to run the tests.

(cherry picked from commit e2cc5b6d)

(cherry picked from commit 3b6281fa)

Simplify the names for the tests, removing the unnecessary
"libgit2-clar" prefix.  Make "all" the new default test run, and include
the online tests by default (since HTTPS should always be enabled).

For the CI tests, create an offline-only test, then the various online
tests.

(cherry picked from commit ce798b25)

(cherry picked from commit 149790b9)

(cherry picked from commit 4c969618)

(cherry picked from commit 0fb8c1d0)

The goal is to let cmake manage the parallelism

(cherry picked from commit 1f4ada2a)

==17851== Invalid free() / delete / delete[] / realloc()
==17851==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==17851==    by 0x60BBE2B: __libc_freeres (in /lib/x86_64-linux-gnu/libc-2.19.so)
==17851==    by 0x4A256BC: _vgnU_freeres (in /usr/lib/valgrind/vgpreload_core-amd64-linux.so)
==17851==    by 0x5F8F16A: __run_exit_handlers (exit.c:97)
==17851==    by 0x5F8F1F4: exit (exit.c:104)
==17851==    by 0x5F74F4B: (below main) (libc-start.c:321)
==17851==  Address 0x63153c0 is 0 bytes inside data symbol "noai6ai_cached"

(cherry picked from commit 234443e3)

==2957== 912 bytes in 19 blocks are still reachable in loss record 323 of 369
==2957==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2957==    by 0x675B120: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x675BDF8: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x675FE0D: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x6761DC4: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x676477E: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x675B071: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x675B544: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x675914B: gcry_control (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==2957==    by 0x5D30EC9: libssh2_init (in /usr/lib/x86_64-linux-gnu/libssh2.so.1.0.1)
==2957==    by 0x66BCCD: git_transport_ssh_global_init (ssh.c:910)
==2957==    by 0x616443: init_common (global.c:65)

(cherry picked from commit dd75885a)

(cherry picked from commit 573c4089)

==18109== 664 bytes in 1 blocks are still reachable in loss record 279 of 339
==18109==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==18109==    by 0x675B120: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==18109==    by 0x675C13C: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==18109==    by 0x675C296: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==18109==    by 0x679BD14: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==18109==    by 0x679CC64: ??? (in /lib/x86_64-linux-gnu/libgcrypt.so.11.8.2)
==18109==    by 0x6A64946: ??? (in /usr/lib/x86_64-linux-gnu/libgnutls.so.26.22.6)
==18109==    by 0x6A116E8: ??? (in /usr/lib/x86_64-linux-gnu/libgnutls.so.26.22.6)
==18109==    by 0x6A01114: gnutls_global_init (in /usr/lib/x86_64-linux-gnu/libgnutls.so.26.22.6)
==18109==    by 0x52A6C78: ??? (in /usr/lib/x86_64-linux-gnu/libcurl-gnutls.so.4.3.0)
==18109==    by 0x5285ADC: curl_global_init (in /usr/lib/x86_64-linux-gnu/libcurl-gnutls.so.4.3.0)
==18109==    by 0x663524: git_curl_stream_global_init (curl.c:44)

(cherry picked from commit c0c9e9ee)

(cherry picked from commit 74b0a432)

(cherry picked from commit 2f4e7cb0)

When executing `libgit2_clar -smerge -invalid_option`, it will first execute
the merge test suite and afterwards output help because of the invalid option.

With this changa, it verifies all options before execute. If there are any
invalid options, it will output help and exit without actually executing
the test suites.

(cherry picked from commit 32758631)

Commit 723e1e97 (appveyor: disable DHE to avoid spurious failures,
2018-03-29) added a workaround to fix spurious test failures due to a
bug in Windows' SChannel implementation. The workaround only worked by
accident, though, as the registry key was in fact mistyped. Fix the
typo.

(cherry picked from commit 3a72b0e2)

Our CI builds have intermittent failures in our online tests, e.g. with
the message "A provided buffer was too small". This is not a programming
error in libgit2 but rather an error in the SChannel component of
Windows. Under certain circumstances involving Diffie-Hellman key
exchange, SChannel is unable to correctly handle input from the server.
This bug has already been fixed in recent patches for Windows 10 and
Windows Server 2016, but they are not yet available for AppVeyor.

Manually pamper over that issue by disabling all ciphersuites using DHE
via the registry. While this disables more ciphers than necessary, we
really don't care for that at all but just want to avoid build failures
due to that bug.

See [1], [2] or [3] for additional information.

1: https://github.com/aws/aws-sdk-cpp/issues/671
2: https://github.com/dotnet/corefx/issues/7812
3: https://support.microsoft.com/en-us/help/2992611/ms14-066-vulnerability-in-schannel-could-allow-remote-code-execution-n
(cherry picked from commit 723e1e97)

In order to cover a wider range of build environments, add two more jobs
which build and test libgit2 on Visual Studio 14 2015.

(cherry picked from commit 03a95bc5)

AppVeyor currently does provide three standard build worker images with
VS2013, VS2015 and VS2017. Right now, we are using the implicitly, which
is the VS2015 one. We want to be more explicit about this, so that we
can easily switch build images based on the job. So starting from this
commit, we explicitly set the `APPVEYOR_BUILD_WORKER_IMAGE` variable per
job, which enables us to choose different images.

To be able to test a wider range of build configurations, this commit
also switches the jobs for VC2010 over to use the older, VS2013 based
images. As the next commit will introduce two new jobs for building with
VS2015, we have then covered both build environments.

Also, let us be a bit more explicit regarding the CMake generator.
Instead of only saying "Visual Studio 10", use the more descriptive
value "Visual Studio 10 2010" to at least avoid some confusion
surrounding the versioning scheme of Visual Studio.

(cherry picked from commit e1076dbf)

Some tests shall be run against our own SSH server we spin up in Travis.
As those need to be run separate from our previous tests which run
against git-daemon, we have to do this in a separate step. Instead of
bundling all that knowledge in the CI script, move it into the test
build instructions by creating a new test target.

(cherry picked from commit 5874e151)

Right now, we test our credential callback code twice, once via SSH on
localhost and once via a non-existent GitHub repository. While the first
URL makes sense to be configurable, it does not make sense to hard-code
the non-existing repository, which requires us to call tests multiple
times. Instead, we can just inline the URL into another set of tests.

(cherry picked from commit 54a1bf05)