Another attempt at fixing Logout. It's more secure now, but not very user friendly. If Anonymous browsing is disabled, all is well. But if anonymous browsing is enabled, hitting logout still forces a login prompt. The user has to hit Cancel to get back to anonymous.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2571 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9