new directive SSIUndefinedEcho.
this allows webadmins to change the default '(none)' to something
a bit more presentable (eg <!-- undef -->)
PR:
Obtained from: Rex (the hack he had to fix this was so ugly I was forced to do this)
Submitted by:
Reviewed by:


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93788 13f79535-47bb-0310-9956-ffa450edef68