Quantum-erase GraphicsLock; Some changes needed to accomplish this:

* comm/trackplayer Callbacks are now queued instead of asynchronously called on the stream decoder thread
* libs/callback now guards the list with a mutex (called from different threads)
* only one thread (Starcon2Main) is allowed to queue draw commands right now; a sanity check is in place (define DEBUG_DCQ_THREADS)
Fixes: Alarms and Callbacks are used for more than just Netplay, reflect this.

git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@3761 8092fc87-c524-0410-9efc-e669fe64eaf9

sc2/doc/devel/threads

@@ -97,10 +97,7 @@ The simplest form of lock.  If a thread tries to lock a mutex, it will
 sleep if the mutex is already locked, and awaken once the mutex
 becomes available.  A Mutex must be unlocked by the same thread that
 locked it, and a thread must never lock a mutex it has already locked
-(without unlocking it first).  The most important Mutex in the program
-the GraphicsLock.  Code in UQM that does things like change the
-screen's clipping rectangle always grabs the GraphicsLock first, to
-ensure that the screen doesn't go crazy.
+(without unlocking it first).
 
 API:
 Mutex CreateMutex (const char *name, DWORD syncClass);