* IMuse is no longer a concurrency front-end.
* IMuseInternal now derives from IMuse.
* Common::StackLock used to protect thread-sensitive interface methods (same as IMuseDigital).
* clear_queue() included in stopAllSounds() so it can be removed from the public interface.
* Game ID now specified at init using property().
* Timer callbacks receive a struct containing IMuseInternal and MidiDriver refs, instead of just the latter.
* OSystem pointer from init is now cached and used instead of global.
All references to the g_system and g_scumm globals are now gone. BOOYAH!
Tested with MI2, DOTT and S&M, under Windows, in Native MIDI, Adlib, and Mixed modes. No regressions or concurrency issues observed. Manifestations of the latter are the biggest concern at this point.
svn-id: r21104
