After signalling an event, always wait for the signalled thread to touch

m_WaitersDone.  This fixes problems with

 event.Lock();
 event.Signal();
 while(x) event.Wait();

picking up the signal that it just sent (which is wrong), especially in the
debugger.

stepmania/src/arch/Threads/Threads_Win32.h

@@ -57,7 +57,6 @@ private:
 	CRITICAL_SECTION m_iNumWaitingLock;
 	HANDLE m_WakeupSema;
 	HANDLE m_WaitersDone;
-	bool m_bNeedSignal;
 };
 
 class SemaImpl_Win32: public SemaImpl