title: ggplot2 reverse order of scale_brewer
body: <p>Seemingly a very simple thing to do but it took me >30min without finding answer.</p>
  
  <p>How do I reverse the order of colors?  By looking at <a href="http://www.had.co.nz/ggplot2/scale_brewer.html">documentation for scale_brewer</a>, i figured it can be <code>formatter=</code> argument being suspicious.  I passed <code>'rev'</code> and then <code>rev</code>, but they have no effect (no error message, just ignored).</p>