graph.CmdPush: plumbing a /v2/ POC
Added registry v2 server impl
Merge branch 'vbatts-v2_hacking' of github.com:vbatts/docker into vbatts-v2_hacking

Conflicts:
	graph/push.go
	registry/v2/routes/router.go
Merge branch 'vbatts-v2_hacking' of github.com:vbatts/docker into vbatts-v2_hacking
graph CmdPush: fixing the bad merge