title: Add title text to legend block in octave
body: <p>I'm trying to add a title to the legend block in a plot I've got in Octave (<a href="http://i.stack.imgur.com/vR9MR.png" rel="nofollow">like this</a>). I've had a dig through the properties that are available on the plot and have found the 'title' attribute, but when I set it there's no change on the plot. </p>
  
  <p>Here's an example of what I'm trying:</p>
  
  <pre><code>a=linspace(0, 2*pi())
  h=plot(sin(a))  
  hleg = legend("Data 1")
  set(hleg, 'title', 'Data Series')
  </code></pre>
  
  <p>I've also tried this:</p>
  
  <pre><code>hlegtitle = get(hleg, 'title') 
  get(hlegtitle, 'string')
  </code></pre>
  
  <p>which returns <code>Data Series</code>, so I'm clearly setting the property, but the title does not appear on the legend. </p>
  
  <p>Is there something else that needs to be set somewhere -- is the title block being drawn off-screen, or is there a boolean or something that causes it to be hidden I've compared the various properties on <code>hlegtitle</code> with those for other components of the plot, and they all seem the same.</p>
  
  <p>Is there something that I'm missing, or is this just not possible?</p>