Make life happy for people who don't have serf but

still use most... yeah, this means you need to explicitly
add mod_serf... no, this isn't a comment on how cool
mod_serf is :)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@594586 13f79535-47bb-0310-9956-ffa450edef68