New config option (mail_priority): if use_x_priority is set to ON, what should the value of X-Priority be? The default is 3 (instead of 0 in previous version, which was misinterpreted by some MTAs)

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1907 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9