v0.4.1 - sound fixes

Small fixes on top of v0.4.0.

• Ambient sounds are capped to 2 of the 4 channels. Wind, jungle and
  industry noise can no longer take the whole hardware and drown out
  construction and vehicles.
• Hard-panned sounds are audible again. Volume used whichever side the
  channel happened to sit on, so a sound panned fully the other way got exactly
  zero and was silent.
• Finished sounds are collected every tick, not only when a new sound is
  requested, so channels come back promptly.
• The version is on the splash screen, top-right of the picture, so you can
  see which build you are running.
• The complete source diff is now in the repository (patches/). 23 files
  of ours were only ever in a local build tree; GPL v2 wants the corresponding
  source, and now it is there.

Requirements unchanged: 68030 with an FPU minimum, 68040/40 recommended,
68060/50 for full speed. AGA, 16 MB Fast RAM, AmigaOS 3.0/3.1.

Sound effects are on by default (-s amiga); -s null for silence. Music is
still not implemented.

Unpack anywhere and run openttd from a Shell, keeping splash.dat beside it.
OpenGFX and OpenSFX are bundled — nothing from the original TTD is needed. See
LICENCES.txt for what is in the archive and under what terms.