Disabled JMenu not always painted disabled

[weisJ]

If a JMenu overwrites isEnabled to return false without calling setVisible it doesn't get painted disabled. Of course if this happens while the menu is already shown this is expected, but a menu which already reports this upon first being painted (e.g. by returning false before the popup menu is visible) should still be painted disabled.

This comes in handy if once wants to have a JMenu be disabled if it has no children. The question would be if we simply always paint JMenus disabled if they have no child items (with a flag to change this behaviour if desired).