title: Why Sourcetree does not support the use of '/' in Git-flow branch names?
body: <p>When I try to create a new feature I press <strong>Git-flow -> Start New Feature</strong> and if I chose a branch name like this: <em>model/user</em> in the end the complete branch name should be <strong><em>feature</strong>/model/user</em> but instead I get an error: </p>
  
  <pre><code>The name is invalid. Ref names must follow git ref-format rules: 
  https://www.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html
  Additionally Sourcetree does not support the use of '/' in Git-flow branch names
  Completed with errors, see above.
  </code></pre>
  
  <ul>
  <li><p>SourceTree version: <strong>3.1.3</strong></p></li>
  <li><p>Git-flow version: <strong>1.11.0 (AVH Edition)</strong></p></li>
  </ul>
  
  <p>Before this update branch names could contain '/' and were displayed as an arborescent structure.</p>
  
  <p>If I use <a href="https://gist.github.com/JamesMGreene/cdd0ac49f90c987e45ac" rel="nofollow noreferrer">git flow commands</a> it works and new branch appears in SourceTree.</p>
  
  <p>Is this a bug or it's a normal behaviour?</p>