[crossfire] Sound support on GTKv2

[Kevin Zheng]

Hi there,

A big element missing from Crossfire is sound. While sound support has
existed for quite a long time, it has consistently failed to work on
newer installations. In addition, sound files have remained untouched
for many releases. I intend to fix this.

A quick glance through the client sound sources show that a great deal
of effort has been put through to make it work with several major sound
systems out there. While supporting many sound systems is good, it has
become overly cumbersome and makes the source hard to work with.

For this reason, I propose that sound support should be discontinued for
every system except for SDL_mixer. SDL_mixer is a high-level library
that supports ALSA, OSS, and many other lower-level sound systems.
SDL_mixer also supports OGG, which enables us to use a higher-level
sound format other than the raw PCM file we use today. Hopefully this
will make sound contributions easier, too.

I would like to be able to start working on the code changes in the very
near future. Questions/comments/hate mail?

Thanks,
Kevin Zheng