mpd uses some additional files to work, such as pid_file, state_file,
db_file, etc. when running mpd as non-root user, it is often that those
files end in ~/.mpd

in that case, we end up with 2 entries in a user's home, .mpdconf and
.mpd - which clutters homedirs.

this patch allows ~/.mpd/mpd.conf as an alternative to ~/.mpdconf,
allowing for a cleaner homedir