
Menubar menu entry problems:
  Unix
    - motion events and keyboard traversal could leave menu posted
    - keyboard traversal didn't skip non-existent entry 0
    - draws oversized checkbutton / radiobutton indicators
    - fails to invoke command / checkbutton / radiobutton in menubar
  Windows
    - does not draw indicator for checkbutton / radiobutton
    - shows "(Image)" instead of the photo or bitmap given for -image,
      shows "(Pixmap)" instead of the bitmap supplied for -bitmap.
      The following excerpt from menu(n) man page implies that images
      are unsupported only for the system menu:

       "Due to  limitations in the Windows API, any font changes, colors,
        images, bitmaps, or tearoff images will not appear in the system
        menu."
