Use Obvious/groupcache instead of golang/groupcache

Hello @dpup, 

Please review the following commits I made in branch 'chad-useObviousGroupcache'.

3a45bb0eaf2f49f66cfc5b032c9c82e9fd846445 (2013-09-27 13:46:02 -0700)
Use Obvious/groupcache instead of golang/groupcache.

Check list:


R=@dpup
VISIBLE_CHANGES=Use Obvious/groupcache instead of golang/groupcache