enable stack traces if you have the xdebug module loaded into php

see: http://www.jdimedia.nl/derick/xdebug.php to get this module

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1352 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9