Added thread_wait_for_count() which allows the menu to wait for all (new) threads to

exit before continuing. We need this for khu testing because we have to make sure
cleanup is done before getting the used byte count.

kern/include/thread.h

@@ -178,5 +178,7 @@ void schedule(void);
  */
 void thread_consider_migration(void);
 
+extern unsigned thread_count;
+void thread_wait_for_count(unsigned);
 
 #endif /* _THREAD_H_ */