title: Joda time, Period to total millis
body: <p>I'm trying to get the <em>total</em> amount of Milliseconds (<em>not</em> the millis field) from the Period object instance. I've tried multiple conversions, as I couldn't find any method easily giving it.</p>
  
  <p>Has anyone ever needed that and managed to retrieve it ?</p>
  
  <p>(I need this for my patch, to figure out a negative period; negative millis = negative period.)</p>