Switch to using `git_reference_iterator`.
Make sure that we also free memory in case an exception happens in ruby land.
This is no longer used.
Better naming.
Remove unused var warning.
Eh, I guess this is correct now.
Merge pull request #213 from arthurschreiber/patch-1

Remove unused var warning.
Merge pull request #212 from arthurschreiber/use_ref_iterator

Use ref iterator
bump libgit2 to 63908c
bump libgit2 to 8baca1