title: running matplotlib with no DISPLAY
body: <p>When matlplotlib run (from summarize_taxa_through_plots.py) I got the error:</p>
  
  <pre><code>...
   raise RuntimeError('Invalid DISPLAY variable')
  RuntimeError: Invalid DISPLAY variable
  </code></pre>
  
  <p>I saw this problem in a lot of sites, the solution is to change user's matplotlirc or global one: </p>
  
  <pre><code>backend:qt4agg
  </code></pre>
  
  <p>to</p>
  
  <pre><code>backend:agg
  </code></pre>
  
  <p>I change the global matplotlibrc.</p>
  
  <p>Now when I run the program use matplotlib I get:</p>
  
  <pre><code>Command returned exit status: 1
  Stdout:
  
  Stderr
  Traceback (most recent call last):
    File "/path/to/python/2.7.6/bin/plot_taxa_summary.py", line 278, in &lt;module&gt;
      main()
    File "/path/to/python/2.7.6/bin/plot_taxa_summary.py", line 274, in main
      resize_nth_label, label_type, include_html_legend)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/qiime/plot_taxa_summary.py", line 1138, in make_all_charts
      resize_nth_label, label_type, include_html_legend))
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/qiime/plot_taxa_summary.py", line 1073, in get_counts
      label_type, include_html_legend))
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/qiime/plot_taxa_summary.py", line 861, in make_HTML_table
      props={'title': title})
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/qiime/plot_taxa_summary.py", line 662, in make_area_bar_chart
      background_color, img_abs, generate_image_type, dpi)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/qiime/plot_taxa_summary.py", line 187, in make_legend
      shadow=False, fancybox=False)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/figure.py", line 1251, in legend
      l = Legend(self, handles, labels, *args, **kwargs)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/legend.py", line 385, in __init__
      self._init_legend_box(handles, labels, markerfirst)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/legend.py", line 654, in _init_legend_box
      fontsize, handlebox))
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/legend_handler.py", line 119, in legend_artist
      fontsize, handlebox.get_transform())
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/legend_handler.py", line 252, in create_artists
      self.update_prop(p, orig_handle, legend)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/legend_handler.py", line 78, in update_prop
      legend._set_artist_props(legend_handle)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/legend.py", line 401, in _set_artist_props
      a.set_figure(self.figure)
    File "/path/to/python/2.7.6/lib/python2.7/site-packages/matplotlib/artist.py", line 640, in set_figure
      raise RuntimeError("Can not put single artist in "
  RuntimeError: Can not put single artist in more than one figure
  </code></pre>
  
  <p>Any idea?</p>