Curl by default does not report errors by setting the error code.
As the upload can fail through several conditions (e.g. the rate
limit, leading to unauthorized access) we should indicate this
information in Travis CI.

To improve upon the behavior, use `--write-out=%{http_code}` to
write out the HTTP code in addition to the received body and
return an error if the code does not equal 201.

When the user passes in a diff which has no repository associated
we may call `git_config__get_int_force` with a NULL-pointer
configuration. Even though `git_config__get_int_force` is
designed to swallow errors, it is not intended to be called with
a NULL pointer configuration.

Fix the issue by only calling `git_config__get_int_force` only
when configuration could be retrieved from the repository.

In C89 it is undefined behavior to pass `NULL` pointers to
`strncmp` and later on in C99 it has been explicitly stated that
functions with an argument declared as `size_t nmemb` specifying
the array length shall always have valid parameters, no matter if
`nmemb` is 0 or not (see ISO 9899 §7.21.1.2).

The function `str_equal_no_trailing_slash` always passes its
parameters to `strncmp` if their lengths match. This means if one
parameter is `NULL` and the other one either `NULL` or a string
with length 0 we will pass the pointers to `strncmp` and cause
undefined behavior.

Fix this by explicitly handling the case when both lengths are 0.

When computing a short OID we do this by first copying the
leading parts into the new OID structure and then setting the
trailing part to zero. In the case of the desired length being
`GIT_OID_HEXSZ - 1` we will call `memset` with an out of bounds
pointer and a length of 0. While this seems to cause no problems
for common platforms the C89 standard does not explicitly state
that calling `memset` with an out of bounds pointer and
length of 0 is valid.

Fix the potential issue by using the newly introduced
`git_oid__cpy_prefix` function.

This fixes an issue in Xcode 7.3 in objective-git where we get the error
"Include of non-modular header file in module". Not importing this
header again fixes the issue.

When parsing a section header we expect something along the
format of '[section "subsection"]'. When a section is
mal-formated and is entirely missing its quotation marks we catch
this case by observing that `strchr(line, '"') - strrchr(line,
'"') = NULL - NULL = 0` and error out. Unfortunately, the error
message is misleading though, as we state that we are missing the
closing quotation mark while we in fact miss both quotation
marks.

Improve the error message by explicitly checking if the first
quotation mark could be found and, if not, stating that quotation
marks are completely missing.

The first time may be due to memory fragmentation or just bad luck on a
32-bit system. When we hit the mmap error for the first time, free up
the unused windows and try again.

When looking up an abbreviated oid, show the actual (abbreviated) oid
the caller passed instead of a full (but ambiguously truncated) oid.

The inner packet may be split across multiple sideband packets.

ssh, ssh+git and git+ssh should all successfully build an SSH transport

Also moving var declarations to top of blocks to support bad old compilers

The parser now also supports digits, '-' and '.'. https://github.com/nodejs/http-parser/pull/276

treebuilder: don't try to verify submodules exist in the odb

Submodules don't exist in the objectdb and the code is making us try to
look for a blob with its commit id, which is obviously not going to
work.

Skip the test if the user wants to insert a submodule.

ssh: initialize libssh2

We should have been doing this, but it initializes itself upon first
use, which works as long as nobody's doing concurrent network
operations. Initialize it on our init to make sure it's not getting
initialized concurrently.

Expand OpenSSL and libssh2 thread safety documentation

test: make sure we retry the auth callback on all platforms

xdiff: fix memleak on error case

If the caller has provided bad authentication, give them another
apportunity to get it right until they give up. This brings WinHTTP in
line with the other transports.

We were missing this test on Windows, which meant we didn't notice that
we never fixed the single authentication attempt it tries, nor its wrong
return code.

Enable this for the unix platforms as well over HTTP. We previously were
doing it locally but disabled it on OS X due to issues with its sshd not
accepting password authentication.

Stricter object dependency checking during creation