title: Increase space between axis.title and axis.text in ggplot2 (version >= 0.9.0)
body: <p>I am currently using the latest version of ggplot2 from github.</p>
  
  <p>In version 0.8.9 I could do the following to increase space between axis.title and axis.text:</p>
  
  <p>Before:</p>
  
  <pre><code>ggplot(diamonds, aes(clarity)) + geom_bar() + opts(
      axis.title.x = theme_text(vjust=-1.1)
  )
  </code></pre>
  
  <p><img src="https://dl.dropbox.com/u/38153519/0.8.9.png" alt=""></p>
  
  <p>Fix:</p>
  
  <pre><code>ggplot(diamonds, aes(clarity)) + geom_bar() + opts(
      axis.title.x = theme_text(vjust=-1.1),
      plot.margin = unit(c(1, 1, 0.8, 0.5), "lines")
  )
  </code></pre>
  
  <p><img src="https://dl.dropbox.com/u/38153519/0.8.9_fix.png" alt="link to graph"></p>
  
  <p>and the axis.title becomes fully visible.</p>
  
  <p>In the latest github version of ggplot2 plot.margin has no effect on axis.title:</p>
  
  <pre><code>ggplot(diamonds, aes(clarity)) + geom_bar() + opts(
      axis.title.x = theme_text(vjust=-0.2),
      plot.margin = unit(c(1, 1, 2, 0.5), "lines"))
  </code></pre>
  
  <p><img src="https://dl.dropbox.com/u/38153519/latest.png" alt="link to graph"></p>
  
  <p><em>(notice the increased bottom margin - I can't get plot.background to work in the latest development version)</em></p>
  
  <p>It seems that 0.8.9 allows axis.title to move over the extra space created by plot.margin, but this is not allowed in the latest development version.</p>
  
  <p>Is there a new way to accomplish this task (or a quick fix for it) in the latest development version?</p>
  
  <p>Any help appreciated.</p>