allout key bindings and trailing control-h

[ken manheimer]

i should mention that before the epg migration i checked in a few allout changes affecting keybindings.  one enables the user to assign all allout keybindings, including picking a prefix key sequence and individual key assignments, as customizations.  another controls whether or not a trailing control-h on an allout key sequence is conserved for describe-prefix-bindings, and in keeping with emacs conventions, it defaults to conserving it.

the latter is another fix that was a due for a long time, and one which i believe you, leo, were arguing for.

see the allout-keybindings customization group and allout-preempt-trailing-ctrl-h allout customization variable.

ken