Allow rsync to use other remote shells.

Introduced a new per-remote option 'annex-rsync-transport' to specify
the remote shell that it to be used with rsync. In case the value is
'ssh', connections are cached unless 'sshcaching' is unset.

Remote/Helper/Ssh.hs

@@ -22,9 +22,10 @@ sshToRepo :: Git.Repo -> [CommandParam] -> Annex [CommandParam]
 sshToRepo repo sshcmd = do
 	g <- fromRepo id
 	let c = extractRemoteGitConfig g (Git.repoDescribe repo)
-	let opts = map Param $ remoteAnnexSshOptions c
-	params <- sshParams (Git.Url.hostuser repo, Git.Url.port repo) opts
-	return $ params ++ sshcmd
+	    opts = map Param $ remoteAnnexSshOptions c
+            host = Git.Url.hostuser repo
+	params <- sshCachingOptions (host, Git.Url.port repo) opts
+	return $ params ++ Param host : sshcmd
 
 {- Generates parameters to run a git-annex-shell command on a remote
  - repository. -}