buildrequest collapse
 - TODO:
   - update master/docs/manual/customization.rst
break the brdict loop as soon as possible
 - do not use brdict term
 - use worst_status
 - don't ignore buildset with claimed br
 - Fix pyflakes
 - data.updates.completeBuildRequests have now the responsability of completing the parent buildset
Merge pull request #1261 from delanne/buildrequestcollapse

buildrequest collapse