Fix 0008931: Circle Relations cause roadmap to malfunction.
Roadmap and Changelog have cycle detection now.
When a cycle is detected, one element from the cycle is placed into the roadmap as if it had no parent.
The rest of the cycle is handled as normal.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@5105 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9