#19 extract audio tracks from CD

[Robert Millan]

Support in build.sh to extract audio tracks from CD
(with -m flag).

This depends on my previous patch for FLAC support.

I noticed that sounds.lua defines playsections for the
CD tracks, but these aren't actualy played in the
game. Any idea why?

Anyway, I'd prefer playing them from my flac files in
music/ dir. Anyone know what is the LUA magic to do
this?

[Robert Millan]