Fix unix/posix.h include guard
Only create openssl_locks if thread support is enabled
Solaris doesn't necessarily have stdint.h, use inttypes.h
Merge pull request #2503 from jacquesg/solaris-http-parser

Solaris doesn't necessarily have stdint.h, use inttypes.h
Silence unused variables warnings
Define WINHTTP_IGNORE_REQUEST_TOTAL_LENGTH if not defined
Cleanup portability/compatibility layer

* Removes mingw-compat.h
* Cleans up separation of compiler/platform idiosyncrasies
* Unifies mingw/msvc stat structures and functions
* (Tries to) hide more compiler specific implementation details (even in our internal API)
Consistently use p_snprintf
Use p_snprintf also in tests
Move p_realpath logic to realpath.c
Introduce some consistency in definition/declaration ordering
Fix typo in timer normalization constants

The effect of this would be that various update callbacks would
not be made at the correct interval.
Merge pull request #2471 from jacquesg/compatibility-cleanup

Compatibility/Portability cleanup
Don't report status on named pipes

Git skips entries in directories that are not S_ISDIR, S_ISREG, or
S_ISLNK, so let's make libgit2 do the same thing.
Merge pull request #2506 from libgit2/rb/ignore-pipes-etc

Don't report status on named pipes
Merge pull request #2507 from libgit2/rb/timer-typo

Typo in timer constants
config: a multiline var can start immediately

In the check for multiline, we traverse the backslashes from the end
backwards and int the end assert that we haven't gone past the beginning
of the line. We make sure of this in the loop condition, but we also
check in the return value.

However, for certain configurations, a line in a multiline variable
might be empty to aid formatting. In that case, 'end' == 'start', since
we ended up looking at the first char which made it a multiline.

There is no need for the (end > start) check in the return, since the
loop guarantees we won't go further back than the first char in the
line, and we do accept the first char to be the final backslash.

This fixes #2483.
Merge pull request #2509 from libgit2/cmn/immediate-multiline

config: a multiline var can start immediately
Allow NULL error message prefix when class=GITERR_OS
Merge pull request #2513 from ethomson/giterr_null_msg

Allow NULL error message prefix when class=GITERR_OS