Fallback to defining advice on "command-execute" in emacs trunk

Emacs trunk has changed the advice system, so my fixes for the "advice
on call-interactively" problem no longer apply. So for trunk, we fall
back to advising "command-execute" instead of "call-interactively" and
avoid overriding "called-interactively-p". This misses some cases,
like interactive commands invoked directly via keybindings instead of
e.g. M-x, but it won't break "called-interactively-p".

Once Emacs trunk has stabilized on a new advice system, I will look
into updating my code to handle it properly and fully re-enable
ido-ubiquitous command overrides for Emacs trunk.
Remove message about enabling/disabling mode

"define-minor-mode" already provides this message.
Remove unnecessary "eval-when-compile"