mpd + aucat

[Aaron Stellman]

mpd port creates "_mpd" user and example config suggest to use it.
Recent changes to aucat introduce some problems for mpd and possibly for
other audio ports that run as a separate user. mpd process
tries to connect to /tmp/aucat-560/default and fails. 560 being uid for
_mpd.
Ideally, this needs to be documented and fixed.
thanks