Add entry for the common case of:
xxx: can't open /dev/dsp!
which causes a lot of people new to FreeBSD to wonder why their card seems
to probe and set itself up correctly, but which doesn't play their mp3's.
This is due to Gnome's esound or KDE's sound support to hold the devices
hostage.

Obtained from: Troubleshooting session by yours truly on Undernet #FreeBSD