This was one huge mess where nothing fit together.
Also added an enhancement that the CD Audio boss theme tracks are also played when CD music is generally off, because these have no equivalent in MIDI. This needs to be checked if it's stylistically ok, though.
- consolidated the 3 identical S_OpenAudio implementations. The replacement code is disabled for the time being because it needs a rewrite. The replacement logic is uses is a bit too volatile.
- removed the old GRP scan code.
Note: enet uses 'malloc' and 'free' as field names in a struct - this does not work with any compiler using some sort of heap instrumentation that #defines these names!
This had to be changed to allow MSVC debug builds to compile again.