Fixed 0002517: Security Warnings [on login page if admin folder is accessible, administrator/root account enabled, or PLAIN passwords used].

M login_page.php

• Warning if admin/ folder exists and is-readable.
• Warning if administrator/root account is active.
• Warning if PLAIN passwords are used.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2221 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9