alex dependency in cvs

It would be good to have the configure script fail (or at least give a
warning--saying it's not found doesn't tell me that it is needed) if alex
isn't present.

Also, it would be nice to update the web page to use the CVS version of the
"CVS cheatsheet", since the one that is available online makes no mention
of alex, either as an available CVS module or as a build dependency.
-- 
David Roundy
http://www.abridgegame.org