title: Subversion update externals to a date
body: <p>I'm working on a large, established project under SVN control. Many parts of the code base are being checked out as externals, but are being actively worked on by other people.<br>
  I wanted to update my entire working copy, externals and all, so that it reflected the various repositories' HEADs at a specific point in time. My initial attempt was:</p>
  
  <pre><code>svn up -r'{20090324}'
  </code></pre>
  
  <p>This updates the current directory to the specified date, but updates all externals to the <em>current</em> date. Updating the externals one at a time works as expected.<br>
  I understand that due to the nature of externals, a single update couldn't work with a revision number, but why doesn't it work with a date?<br>
  What's the best way to achieve the point-in-time effect that I'm looking for, without having to maintain a script that hard-codes the various externals?</p>
  
  <p>I'm running a Linux system.</p>