mod_lua: If a regex fails, return false plus an error message as second return...

mod_lua: If a regex fails, return false plus an error message as second return value. Also fix some functions who weren't always returning a value.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1422373 13f79535-47bb-0310-9956-ffa450edef68