title: GIT: merge branch1 and branch2 into master without overwriting
body: <p>I have the following scenario:</p>
  
  <ol>
  <li>Created new branch <code>branch1</code> from <code>master</code></li>
  <li>In <code>branch1</code>, I added a new file called <code>b1.txt</code> + also in <code>common.txt</code> I added new line <code>echo 'line added in branch1';</code>.</li>
  <li>Created new branch <code>branch2</code> from <code>branch1</code></li>
  <li>Renamed the file <code>b1.txt</code> to <code>b2.txt</code> + also in <code>common.txt</code> I changed that line to <code>echo 'line added in branch2';</code>.</li>
  <li>Merged <code>branch1</code> into <code>master</code></li>
  <li>Merged <code>branch2</code> into <code>master</code></li>
  </ol>
  
  <p><strong>Result</strong>: <code>master</code> has 1 new file <code>b2.txt</code>, and new line in <code>common.txt</code> that reads <code>echo 'line added in branch2';</code>.</p>
  
  <p><strong>What I'd like to get as result:</strong> <code>master</code> has 2 new files <code>b1.txt</code> and <code>b2.txt</code>, and 2 new lines in <code>common.txt</code> that reads <code>echo 'line added in branch1';</code> and <code>echo 'line added in branch2';</code>.</p>
  
  <p><strong>How to achieve this?</strong></p>
  
  <p><strong>Note:</strong> I know, normally, I should create <code>branch2</code> from <code>master</code>, but It's much easier to copy-paste (and slightly modify) the changes of <code>branch1</code>, although <code>branch1</code> is not yet merged into <code>master</code>.</p>