title: Build pull request from forked origins in Jenkins
body: <p>I am trying to make Jenkins build the pull request my project receives from forks.</p>
  
  <p>I am using the Github plugin and the Jenkins service in Github and I have checked in my Jenkins:</p>
  
  <pre><code>Build fork PRs
  </code></pre>
  
  <p>But when Jenkins tries to build I get:</p>
  
  <pre><code>ERROR: Couldn't find any revision to build. Verify the repository and branch configuration for this job.
  </code></pre>
  
  <p>Regular branches builds correctly, but for some reason my PR not.</p>