title: Exact figure size in matplotlib with title, axis labels
body: <p>Similar questions have been asked before, but all of my search results don't 
  address my problem.  Take the following example code:</p>
  
  <pre><code>from matplotlib.pyplot import *
  fig = figure(1, figsize=(3.25, 3))
  plot([0,1,5,2,9])
  title('title')
  xlabel('xAxis')
  ylabel('yAxis')
  fig.savefig('test.png',dpi=600)
  </code></pre>
  
  <p>The resulting figure is 2040x1890 pixels, or 3.4"x3.15", and the x-label
  is cut off.  Looking at the PNG file in an image editor, it appears that 
  the axes and tick labels fit the desired size.  I've tried taking the 
  difference from the output size and requested size and feeding that back 
  in (3.25 - (3.4-3.25) = 3.10, but matplotlib seems to add an arbitrary 
  buffer and it still doesn't come out to the desired size.  How does one 
  make an overall figure that is the desired size?</p>