git-lfs: remember urls, and autoenable remotes using known urls

* git-lfs: The url provided to initremote/enableremote will now be
  stored in the git-annex branch, allowing enableremote to be used without
  an url. initremote --sameas can be used to add additional urls.
* git-lfs: When there's a git remote with an url that's known to be
  used for git-lfs, automatically enable the special remote.

Git/Remote.hs

@@ -51,6 +51,7 @@ makeLegalName s = case filter legal $ replace "/" "_" s of
 	legal c = isAlphaNum c
 	
 data RemoteLocation = RemoteUrl String | RemotePath FilePath
+	deriving (Eq)
 
 remoteLocationIsUrl :: RemoteLocation -> Bool
 remoteLocationIsUrl (RemoteUrl _) = True