dios: Report an error if a thread terminates while holding a lock.

dios/include/sys/thread.h

@@ -351,7 +351,10 @@ static inline void releaseThread( _PThread &thread )
 
 static inline void releaseAndKillThread( __dios_task tid )
 {
-    releaseThread( getThread( tid ) );
+    auto &thread = getThread( tid );
+    if ( thread.refcnt != 1 )
+        __dios_fault( _VM_Fault::_VM_F_Locking, "thread terminated while holding a lock" );
+    releaseThread( thread );
     __dios_kill( tid );
 }