++libgit2 to hf/master_patch
Remove git_push_unpack_ok check

The function no longer exists. See
libgit2/libgit2@4eb97ef3bf18403fbce351ae4cac673655d2886a.
Refactor GTTreeBuilder to accept a repo on init

Required by libgit2 changes.
Merge pull request #429 from libgit2/bump-libgit2

Bump libgit2 to hf/master_patch