Fixed 0003568: Monitor deleted bugs? [monitor records are not deleted on bug deletion]

M core/bug_api.php

• (bug_unmonitor): support value null for $p_user_id to unmonitor the specified bug for all users.
• (bug_delete): call bug_unmonitor( $p_bug_id, null ) to delete all monitor entries for the bug being deleted. That's done after the email notification is done.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2371 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9