title: matplotlib backend pgf version unknown
body: <p>I'm getting a debug message from <code>matplotlib</code> with the <code>pgf</code> backend:</p>
  
  <pre><code>matplotlib.backends DEBUG backend pgf version unknown
  </code></pre>
  
  <p>My matplotlib setup is something like</p>
  
  <pre><code>mpl.use("pgf")
  mpl.rc('text', usetex=True)
  mpl.rcParams['pgf.rcfonts'] = False
  mpl.rcParams['pgf.texsystem'] = 'xelatex'
  mpl.rcParams["pgf.preamble"] = # xelatex fonts setup and other stuff
  </code></pre>
  
  <p>Is there a way to silent this message? maybe require a specific pgf version?</p>