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.

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.

Script to set up dependencies on a macOS build system.

Sets up a linux host to prepare for a build.

Refactor citest.sh to enable local testing by developers.

Add citest.ps1 PowerShell script to run the tests.

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.

mbedtls: remove unused variable "cacert"

In commit 382ed1e8 (mbedtls: load default CA certificates, 2018-03-29),
the function `git_mbedtls_stream_global_init` was refactored to call out
to `git_mbedtls__set_cert_location` instead of setting up the
certificates itself. The conversion forgot to remove the now-unused
"cacert" variable, which is now only getting declared to be free'd at
the end of the function. Remove it.

Squash some leaks

Instead of allocating the ciphers_list, make it a static array.  This
prevents us from leaking it or having to manage its memory.

Don't just free the spec vector, also free the specs themselves.

Don't just free the push status structure, actually free the strings that were
strdup'd into the struct as well.

Free the url field when resetting the stream to avoid leaking it.

Add a checkout example

Assorted Coverity fixes

Remove GIT_PKT_PACK entirely

 ignore: improve `git_ignore_path_is_ignored` description Git analogy

alloc: don't overwrite allocator during init if set

If the allocator has been set before we the library is initialised, we would
replace that setting with the standard allocator contrary to the user's wishes.

C90 standard compliance

In attempt to provide adequate Git command analogy in regards to
ignored files handling, `git_ignore_path_is_ignored` description
mentions doing `git add .` on directory containing the file, and
whether the file in question would be added or not - but behavior of
the two matches for untracked files only, making the comparison
misleading in general sense.

For tracked files, Git doesn't subject them to ignore rules, so even
if a rule applies, `git add .` would actually add the tracked file
changes to index, while `git_ignore_path_is_ignored` would still
consider the file being ignored (as it doesn't check the index, as
documented).

Let's provide `git check-ignore --no-index` as analogous Git command
example instead, being more aligned with what `git_ignore_path_is_ignored`
is about, no matter if the file in question is already tracked or not.

See issue #4720 (git_ignore_path_is_ignored documentation
misleading?, 2018-07-10)[1] for additional information.

[1] https://github.com/libgit2/libgit2/issues/4720