Fix key bindings.

Fix key bindings.
(electric-help-mode): Use mouse-leave-buffer-hook.
(electric-help-retain): Remove mouse-leave-buffer-hook.
(with-electric-help): New argument minheight.
(electric-help-execute-extended): New function.
(electric-help-ctrl-x-prefix): New function.
(electric-help-command-loop): Make messages more consistent.
Include strategic sit-for 0, so that
pos-visible-in-window-p will return the right thing.
Make 2nd arg of Electric-command-loop return 'noprompt if we
are in isearch-mode.
Eval to-be-executed at the very end.
(ehelp-map): Electrify apropos too.