Release the GVL when pushing.
Release the GVL when pushing.

The GVL is only released if we're running on Ruby 1.9+ and libgit2 was
actually built with threadsafety.

tpickett66/rugged,libgit2/rugged,Acidburn0zzz/rugged,saraid/rugged,saraid/rugged,spraints/rugged,Acidburn0zzz/rugged,tpickett66/rugged,Acidburn0zzz/rugged,spraints/rugged,libgit2/rugged,libgit2/rugged,saraid/rugged,tpickett66/rugged