++libgit2
Replace "orphan" terminology with "unborn"
Modernize, remove cruft from NSError+Git
Don't crash on nil descriptions in +git_errorFor:
Merge pull request #263 from libgit2/update-libgit2

Update libgit2
Use one line for travis build notifications.
withAdditionalDescription: -> description:
Merge pull request #264 from libgit2/error-dictionary

Don't crash on nil descriptions in +git_errorFor:
Merge branch 'master' into git-cred

Conflicts:
	Classes/Categories/NSError+Git.m
Move `-DGIT_SSH` at the project level.
Provide the paths to the public and private keys in the error message.
No need for formatting.
Style: explicit nil comparison.