Fixes by terrencehill and me:

Fixes by terrencehill and me:
- better remapping handling of mixed fake and real cdtrack remappings
- fixed bgmvolume handling with CDs
- resume CD audio before stopping (SDL requires that)
- "cd" command showing help
- "cd reset" now always stops
- "cd rescan" command (don't ask me what it's good for)
- apparently work around SDL bug with looping CD tracks after pause and resume

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@8959 d7cf8633-e32d-0410-b094-e92efae38249