Fixed bug #741

The thread ID is an unsigned long so it can hold pthread_t so people can do naughty things with it.

I'm going to be adding additional useful thread API functions, but this should prevent crashes in people's existing code on 64-bit architectures.

src/thread/beos/SDL_systhread.c

@@ -84,10 +84,10 @@ SDL_SYS_SetupThread(void)
     SDL_MaskSignals(NULL);
 }
 
-Uint32
+SDL_threadID
 SDL_ThreadID(void)
 {
-    return ((Uint32) find_thread(NULL));
+    return ((SDL_threadID) find_thread(NULL));
 }
 
 void