Apply r641391 from trunk [Warning about SetEnv lateness]

          not be a number. Characters which do not match this

          restriction will be replaced by an underscore when passed to

          CGI scripts and SSI pages.</li>

          <li>The <directive module="mod_env">SetEnv</directive> directive runs

          late during request processing meaning that directives such as

          <directive module="mod_setenvif">SetEnvIf</directive> and <directive

          module="mod_rewrite">RewriteCond</directive> will not see the

          variables set with it.</li>

        </ul>

    </section>

  </section>