Remove redundant advice on command-execute

This used to be necessary because it called call-interactively in C
code, where advice is not used, but now it does a proper lisp call to
call-interactively, so the advice on that gets used no matter what.
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"
Revert to from cl-loop to loop and require cl at runtime

cl-loop was introduced in 24.3, so for compatibility with earlier 24.x
versions we need to use just "loop".

The "eval-when-compile" trick seems too fragile, causing cryptic
errors that I dont understand, so I have removed it. These may be
related to some difference between the "cl-*" macros and their
unprefixed aliases. If someone submits a patch showing the correct way
to do the eval-when-compile trick while maintaining compatibility with
the entire version 24.x series, I'll happily merge it.
Remove use of "macroexp--backtrace", which doesn't exist before 24.3

Fixes #26 for emacs versions before 24.3.
Remove override for "man" command

This is now covered by the execption for collection being a function,
so there is no functional change.
Version 2.2