title: ggplot2, facet_grid, free scales?
body: <p>In the following example, how do I get the y-axis limits to scale according to the data in each panel?</p>
  
  <pre><code>mt &lt;- ggplot(mtcars, aes(mpg, wt, colour = factor(cyl))) + geom_point() 
  </code></pre>
  
  <p>Neither of these will do it:</p>
  
  <pre><code>mt + facet_grid(. ~ cyl, scales="free")
  mt + facet_grid(. ~ cyl, scales="free_y")
  </code></pre>