KNOWN BUGS
  - DONE - Circle needs to provide window extent -- see scatter demo
  - DONE - axes patch edge on gtk backend not complete
  - DONE - autoscale on y not satisfactory -- see histogram demo
  - DONE with multiple subplots there is a small gap between the
    bottom of the xtick1 line and the axes patch edge. see
    subplot_demo
  - DONE 2003-11-14 -  lowest line position is off in legend_demo
  - DONE the markers for circ and square in the gtk backend do not have the
    same center.  See the stock_demo for example.
  - DONE 2003-11-16 - GD port of new API not done
  - DONE 2003-11-16 - xticklabels in PS backend need clip
  - x and y ticklabels overlap at origin
  - DONE parse error on lines like plot(bins, mu, bins, mu+sigma, '--')
  - DONE 2004-02-11 mri with eeg offsets whacked
  - add backend method draw ellipse
GD 
  - FIXED right tickline is off
 
  - dashes not scaling with dpi properly - rounding error or other?
  - GD not allocating colors on high res figs 
  
  - I don't know how to fill arcs in a way that will guarantee the
    ellipse will be filled.  gd fills till it meets a different border
    color, which makes it difficult to fill arcs.  expose gdEllipse
    and gdFilledEllipse
FT2
 - chars are truncated on the right, eg, -0.8 in simple_plot
   yticklabels
 - no rotated text
 - error handling