Add specs for MPD.Remote
MPD.Remote: fix module in error calls
MPD.Handle: only try to authenticate for tcp remotes

Previously, we would use the mpdPassword selector on the
conf value, which obviously fails if conf is UnixSocket.
RemoteSpec: readRemote should return full path to unix socket
MPD.Remote: need full path to unix domain socket
Merge branches 'remote-fix-error-calls', 'remote-fix-unix-socket', 'remote-spec' and 'fix-authenticate'