title: Matplotlib's fill_between doesnt work with plot_date, any alternatives?
body: <p>I want to create a plot just like this:
  <img src="https://i.stack.imgur.com/M7jzM.png" alt="This has integer x values"></p>
  
  <p>The code:</p>
  
  <pre><code>P.fill_between(DF.start.index, DF.lwr, DF.upr, facecolor='blue',   alpha=.2)
  P.plot(DF.start.index, DF.Rt, '.')
  </code></pre>
  
  <p>but with dates in the x axis, like this (without bands):
  <img src="https://i.stack.imgur.com/nUyEH.png" alt="with plot_date"></p>
  
  <p>the code:</p>
  
  <pre><code>P.plot_date(DF.start, DF.Rt, '.')
  </code></pre>
  
  <p>the problem is that fill_between fails when x values are date_time objects.</p>
  
  <p>Does anyone know of a workaround? DF is a pandas DataFrame.</p>