title: How to assign exec's output to a property in NAnt
body: <p>My aim is to fill property with output of command "git describe". 
  I have a property:</p>
  
  <pre><code>&lt;property name="build.version" value = ""/&gt;
  </code></pre>
  
  <p>And I want to fill it with output of the following command: <strong>git describe</strong></p>
  
  <p>I tried:</p>
  
  <pre><code>&lt;exec program='${git.executable}' outputproperty='build.version'&gt;
    &lt;arg value='describe' /&gt;
  &lt;/exec&gt;
  </code></pre>
  
  <p>but unlike the Ant, NAnt doesn't support <strong>outputproperty</strong> :( only <strong>output</strong> (to file).</p>