title: Update svn checkout to specific date including externals
body: <p>I want to perform an svn update to a specific date, and I can do this with <code>svn update -r {2010-10-17}</code>.  Unfortunately when this encounters an external it will do the update within the external without passing through the <code>-r {2010-10-17}</code> option.  This results in us getting the correct past revision of the base code, but the latest (undesired) versions of many of the externals.</p>
  
  <p>How can I update to a specific revision or date and have this recurse correctly through the externals?</p>
  
  <p>(Note: I understand that the mistake here might have been to use externals with no explicit revisions specified.)</p>