fix path disclose problem in functions.php

fix path disclose problem in functions.php
don't display system information, if plugin is disabled.
use squirrelmail option widgets instead of own functions. Option saving is
handled by sm.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@9785 7612ce4b-ef26-0410-bec9-ea0150e637f0