RaiseLower: ignore windows on other monitors

When deducing if the windows in the stack ring should be compared
against, only consider those windows on the same monitor as the current
window.

Fixes #86

fvwm/stack.c

@@ -1511,6 +1511,7 @@ static Bool is_on_top_of_layer_ignore_rom(FvwmWindow *fw)
 {
 	FvwmWindow *t;
 	Bool ontop = True;
+	struct monitor *m = fw->m;
 
 	if (IS_SCHEDULED_FOR_DESTROY(fw))
 	{
@@ -1523,6 +1524,9 @@ static Bool is_on_top_of_layer_ignore_rom(FvwmWindow *fw)
 	}
 	for (t = fw->stack_prev; t != &Scr.FvwmRoot; t = t->stack_prev)
 	{
+		if (t->m != m)
+			continue;
+
 		if (t->layer > fw->layer)
 		{
 			break;