Fix for 2884: attachments on closed bugs can be deleted.

M core/file_api.php
(file_list_attachments): Only display [delete] link if the user has handler
access level + the bug status is below the resolved threshold.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1781 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9