Remove unus(ed|ual) ssasn function to fix warnings

Why in tarnation would you assign an int to a string anyway?  We're
apparently not using this, so remove it for now.  Should fix a lot of
unused-parameter warnings.
Add skeletal sound driver for JACK

This doesn't make any sound yet, but it creates the JACK client and connects
the requested ports if any.
Add deinterlacing function to RageSoundMixBuffer

JACK processes every channel separately, so we need this.  The audio data is
interlaced all the way back at RageSound::GetDataToPlay(), so this is an easier
hack for now than using deinterlaced until it's needed.
Add MixDeinterlaced to RageSoundDriver

This complements the read_deinterlace function just added.
Add JACK sample rate callback

This will be necessary once we start the decoding thread, which calls
GetSampleRate a lot.
Finish JACK audio driver: now with actual audio!
Fix stereo problem - samples, not frames
Update IRC channel
woooooooooah changelog.

Add yo stuff if I forgot anything (or anyone!).