further fix for 0005662: 0005641: Re-report: Private projects don't allow
users who have been added to the project use the project...

• improved pruning of project list tree

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3573 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9