bad url shortening

Hi.

Upon CVS commit #29524 and #29525 the preg_replace() stuffs were moved into separate functions, such as urlfilter_replace1() and urlfilter_trim(). And there's a small typo(?) in urlfilter_trim() function, i.e. substr($text, $urlfilter_length) should be substr($text, 0, $urlfilter_length).