Audio volume control.

[Rob Landley]

1) When I plug in USB headphones, it doesn't make them the default device.
(Sometimes the output switches to it, but the volume control doesn't.) I have to
click the speaker icon, click audio mixer, click output devices, scroll down to
headphones, click the green checkbox, and THEN it's the default device.

If you click the speaker icon to open the volume slider, the volume up/down keys
on the keyboard are ignored until you close it again.

Rob