Add Blob#diff.
Update libgit to pull/1657.
Add old_path / new_path options to Blob#diff.
Merge pull request #223 from arthurschreiber/blob_diff

Add Blob#diff.
bump libgit2 to ffb762
bump libgit2 to 84ba49
bump libgit2 to 514485
bump libgit2 to 8b2fa1
Fix some warnings on Ruby 1.8.
bump libgit2 to f2d110
bump libgit2 to 00197c
bump libgit2 to 5d669f
bump libgit2 to 9f1b2c