title: Legend properties when legend.only=T (raster package)
body: <p>When plotting only the legend (of a <code>raster</code> object - a colorbar):</p>
  
  <pre><code>require(raster)
  r = raster()
  r[] = 1
  plot(r, legend=F)
  plot(r, zlim=c(-10,10), legend.only=T)
  </code></pre>
  
  <p>how can I control the legend axis label size, tick length, and other legend properties? I know I can call <code>par(...)</code> before the last <code>plot()</code> call, but is there a cleaner way?</p>