Added beep to TextFIeld.Invalid() on Mac OS X.

redo/basicctrls_darwin.m

@@ -205,6 +205,9 @@ id textfieldOpenInvalidPopover(id textfield, char *reason)
 	// NSMaxYEdge is the bottom edge when looking (maximum edge in window coordinates)
 	[popover showRelativeToRect:NSZeroRect ofView:toNSView(textfield) preferredEdge:NSMaxYEdge];
 
+	// and beep
+	NSBeep();
+
 	return (id) popover;
 }
 

redo/textfield_darwin.go

@@ -49,7 +49,6 @@ func (t *textfield) OnChanged(f func()) {
 func (t *textfield) Invalid(reason string) {
 	// TODO disable animations if reason is still valid
 	// TODO don't steal focus
-	// TODO beep
 	if t.invalid != nil {
 		C.textfieldCloseInvalidPopover(t.invalid)
 		t.invalid = nil