Fix string API to use PHP 5.1 compatible named patterns.
Sorry, didn't realize the method shown in the PHP manual was specific to PHP 5.2.2+, because that's when they upgrade to PCRE version 7.0, which is what introduced the method of named patterns that is shown in the manual...

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@5750 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9