bug#7691: 24.0.50; x-popup-menu with keymap - :help keyword

[grischka]

> If you have any clever ideas about how to "Pop up a deck-of-cards menu and 
> return user's selection." without blocking, then please share them.

Now that "clever idea" exists as long as GUI toolkits are around:  Don't
use a command loop in your application, use event callbacks.