title: define ant property from environment with default value
body: <p>I would like my build script to act properly for release and development environments.</p>
  
  <p>For this I would like to define a property in ant, call it (e.g.) <code>fileTargetName</code></p>
  
  <p><code>fileTargetName</code> will get it's value from the environment variable <code>RELEASE_VER</code> if it's available, if it is not available it will get the default value of <strong>dev</strong></p>
  
  <p>Help with ant <code>&lt;condition&gt;&lt;value&gt;&lt;/condition&gt;</code> &amp; <code>&lt;property&gt;</code> to get it working is appreciated.</p>