title: Jenkins: Build merge commit for Github Pull requests
body: <p>Github creates a commit that is a merge of the PR branch with the base branch (eg develop) every time the PR branch is pushed to, so that it can show if there are merge conflicts in develop. </p>
  
  <p>Is it possible to get Jenkins to build and run tests (etc) on this commit rather than the head of the PR branch. That way it will will detect any errors that would result from the merge itself.</p>
  
  <p>We can't do an local merge with the develop branch every time as sometimes PR's have a different base branch, or Jenkins needs to get the base branch of that PR and do a local merge.</p>