Blob, Commit, Tag or Tree that cannot be found should return undef
Changes: update
Squashed 'deps/libgit2/' changes from e0af251..8f759ac

8f759ac Merge pull request #2471 from jacquesg/compatibility-cleanup
07d03d3 Introduce some consistency in definition/declaration ordering
662f90e Move p_realpath logic to realpath.c
c7dd0a5 Use p_snprintf also in tests
c983604 Consistently use p_snprintf
2f795d8 Cleanup portability/compatibility layer
d07fd44 Define WINHTTP_IGNORE_REQUEST_TOTAL_LENGTH if not defined
959a93e Silence unused variables warnings
f59a34d Only create openssl_locks if thread support is enabled
529c371 Fix unix/posix.h include guard

git-subtree-dir: deps/libgit2
git-subtree-split: 8f759ac0b373eea9dcec680524a68a527d637937
Merge commit '9f0d25d3b58a7fbd568496e01061e806486096fb' into jacquesg/update-libgit2
Tree.xs: entry_byname() and entry_bypath() should return undef if the entry cannot be found
Changes: update
Merge branch 'jacquesg/update-libgit2'
Changes: update
Reflog.xs: Added entry_count()

* entries() now takes an optional index and count parameter
Documentation fixes
Changes: update