title: OptionParser() display choices when --help in Python
body: <p>I need to create an "interface" to my script such that (runs by crontab):</p>
  
  <ol>
  <li>When --help, terminal will display a list of choices (well formatted, separate by \n)</li>
  <li>allow multiple choices input (comma delimited)</li>
  </ol>
  
  <p>e.g. (something like the following)</p>
  
  <pre><code>python feedAnimals.py --help 
  ...... Choices:
             dog
             cat
             fish
  
  python feedAnimals.py --pets dog,cat,fish
  </code></pre>
  
  <p>Is there anyway to do this with <code>type="choices"</code>?
  Or can I use <code>type="string"</code>? I tried to insert <code>\n</code> between choices under the "help" option, but these seems to be neglected at run time.</p>
  
  <p>Must be python 2.4 compatible :(</p>