The user can test regular expressions for the filter. If they
enter an invalid expression the site will add a form error but it
also throws a warning which will clutter the log and isn't really
needed since the form prevents them from saving such a regex
anyway. Here we stop the test from throwing a warning in these
cases.

It is possible that users will want to alter the regex used by
the module. This change provides an admin form that allows the
regex to be overridden and provides and example of the text being
replaced.