*  Example used in book

*xmenu1  Spring-loaded
*xmenu2  Pulldown, popped up with Command, Popup on Press.  Down on release outside.
*xmenu3  Pulldown, popped up with MenuButton instead of Command, using MenuButton popup code.  Down on release outside.
*xmenu4  Pulldown invoked by Command, with submenu, Using grab mode XtGrabExclusive
*xmenu5  Spring-loaded with submenu, more sophisticated CheckLeftAndPopdownSubmenu, using grab mode XtGrabNonexclusive.

xmenu6   Example of why certain routines can be used to pop up menus.
Attempt at Pulldown identical to xmenu2 except using 
XtCallbackExclusive (callbacks only - no actions).  Doesn't work 
because XtCallbackExclusive calls XtPopup which can't pass the right 
parameters to _XtPopup.  Even if you write your own callback it still 
can't be made to work.  (Moral: this type of menu must use XtMenuPopup 
action.)  This is fixed by XtPopupSpringLoaded.

*xmenu7.  using R4 SimpleMenu, MenuButton, and all three Sme gadgets.

xdialog  Test of XtCallbackExclusive callback for popping up a dialog
box.
