Mod_echo was using raw args instead of a flag to enable and disable

itself.  I believe this is what was causing the module to not be able to
be enabled and disabled on a per-server basis.  This patch makes it use
a flag


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86093 13f79535-47bb-0310-9956-ffa450edef68