url plugin: only chop non-word characters on 404

url plugin: only chop non-word characters on 404

Chopping everything causes long delays for non-existing pages with
long paths. Since the purpose of the retry-with-chop is to get the
right URL when punctuation is added after it, the solution is to
only chop non-word characters. This has to be done on the
unescaped URL because otherwise non-word characters like " that
expand to %22 will not be chopped.