Minor fix to "called-interactively-p" advice
Always advise "call-interactively"

Now that "called-interactively-p" in Emacs trunk can detect when
"call-interactively is advised, there's nothing to work around in
Emacs 24.4 and above. (See
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=3984)

Fixes #29.