Move tag tests to the new collection API.
Move tag tests to the new collection API.

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