title: TextWrangler - replace every second line-break with comma
body: <p>I have a text file containing only text lines like this:</p>
  
  <pre><code>abcdefg
  2009
  hijklmnop
  2012
  </code></pre>
  
  <p>I want to replace every second line-break with a comma. So it should look like this:</p>
  
  <pre><code>abcdefg, 2009
  hijklmnop, 2012
  </code></pre>
  
  <p>How can I do this in TextWrangler?</p>