title: merge before build in jenkins fails but should not
body: <p>I have setup jenkins to build all feature branches in a project and before the build merge them to 'develop' since I'm more interested if the result of the merge builds rather than the feature branch itself.</p>
  
  <p>This seem to work if the feature branch is based of develop HEAD but if the branch off point is before develop HEAD then jenkins says: ERROR: Branch not suitable for integration as it does not merge cleanly</p>
  
  <p>And this would be alright if there was a conflict. But there is no conflict. I have tested the merge manually in the console and the merge is automatically done.</p>
  
  <p>Also if comparing the feature branch and develop in atlassian stash it also shows a clean diff without any conflicts.</p>
  
  <p>I'm lost. Why can't jenkins merge it?</p>