WINGs: Make the test examples to compile

Those examples are optional but currently cannot compile properly.
The compiler is reporting some unused variables and missing header file.

WINGs/Tests/mywidget.c

@@ -64,6 +64,7 @@ static W_Class myWidgetClass = 0;
  */
 W_Class InitMyWidget(WMScreen * scr)
 {
+	(void)scr;
 	/* register our widget with WINGs and get our widget class ID */
 	if (!myWidgetClass) {
 		myWidgetClass = W_RegisterUserWidget();