Fix: Duplicate queries can be generated by history_api.

This decreases view.php by about 10 queries on a test bug here - This probably should be fixed in history_api and not here..

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@4350 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9