Fixed: some window subclasses should not be constrained to the usable screen content

Previously, all window subclasses were constrained to the usable screen content. Unfortunately that included the menu bar window, which ended up appearing below itself!

This commit introduces an ivar that indicates whether instances of the window subclass should be constrained or not.

AppKit/CPMenu/_CPMenuBarWindow.j

@@ -67,6 +67,8 @@
 
     if (self)
     {
+        _constrainsToUsableScreen = NO;
+
         [self setLevel:CPMainMenuWindowLevel];
         [self setAutoresizingMask:CPWindowWidthSizable];