title: Git: How to squash all commits on branch
body: <p>I make new branch from <code>master</code> with: </p>
  
  <pre><code>git checkout -b testbranch
  </code></pre>
  
  <p>I make 20 commits into it.</p>
  
  <p>Now I want to squash those 20 commits. I do that with:</p>
  
  <pre><code>git rebase -i HEAD~20
  </code></pre>
  
  <p>What about if I don't know how many commits? Is there any way to do something like:</p>
  
  <pre><code>git rebase -i all on this branch
  </code></pre>