volume control slider behaviour is hazardous

[Michael Norris]

The behaviour of the Volume Control slider in response to click-and-hold is:
- if the cursor is over the slider knob, the slider follows horizontal dragging
otherwise:
- if the cursor is to the left of the slider knob, the volume decreases towards zero
- if the cursor is neither left nor right of the slider knob, nothing happens
- if the cursor is to the right of the slider knob, the volume increases towards maximum

This behaviour is wrong enough to seriously damage equipment and hearing.

Why? - because if you are listening to music and want to increase the volume slightly,
you need to click exactly on the slider knob. If you miss and click just to the right of it
the volume increases way past the horizontal position of the cursor, and if you don't lift
your finger fast enough it will go to maximum volume.

A conservative fix to this behaviour would be:
- if the user clicks and holds when the cursor is above the slider, the slider knob should
move towards, and then track the horizontal cursor position.

Ideally, however, the simple slider should be replaced with something more usable,
and perhaps even prettier.