title: Python argparse fails to parse hex formatting to int type
body: <p>I have the following code which attempts to get the DUT VID from the invoked command line:</p>
  
  <pre><code>parser = argparse.ArgumentParser(description='A Test',
                                   formatter_class=argparse.ArgumentDefaultsHelpFormatter
                                   )
  group.add_argument("--vid",
                     type=int,
                     help="vid of DUT")
  options = parser.parse_args()
  </code></pre>
  
  <p>Consider the command line "python test.py --vid 0xabcd" 
  I notice that argparse is raising an exception on this as it fails to complete the call <code>int('0xabcd')</code> because it is base 16.  How do I get argparse to correctly handle this?</p>