Switch WIN32 to this implementation to be able to use condition
variables, which is impossible with CriticalSection.

The main_cond variable was completely unnecessary.  The pc.cond object
can be used for both main->pc and pc->main.

Don't let the "client" pass its own GCond.  This was not used
consistently.

Fixes potential dead lock bug.

Use a bit field instead of a mutex-protected bool array.

Use std::list instead of GList.

Should fix the OS X build.

The check for unsigned underflow is fragile and unreliable.