title: skimage.io.imshow does not display image
body: <p>I am facing a problem of not able to display image with the following command:</p>
  
  <pre><code>from skimage import io
  io.imshow('abc.png')
  </code></pre>
  
  <p>It shows following error:</p>
  
  <pre><code>/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.pyc in     new_figure_manager(num, *args, **kwargs)
   78     FigureClass = kwargs.pop('FigureClass', Figure)
   79     figure = FigureClass(*args, **kwargs)
  ---&gt; 80     window = Tk.Tk()
   81     canvas = FigureCanvasTkAgg(figure, master=window)
   82     figManager = FigureManagerTkAgg(canvas, num, window)
  
  /usr/lib/python2.7/lib-tk/Tkinter.pyc in __init__(self, screenName, baseName, className, useTk, sync, use)
   1686                 baseName = baseName + ext
   1687         interactive = 0
   -&gt; 1688         self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
   1689         if useTk:
   1690             self._loadtk()
   TclError: no display name and no $DISPLAY environment variable
  </code></pre>
  
  <p>I am running this in remote server. In the server, I found the DISPLAY variable is not set. 
  How do I set the display variable to display the image.</p>