mod_deflate should be merging the Vary header, not Setting it, and ignoring...

mod_deflate should be merging the Vary header, not Setting it, and ignoring what other modules put there.

Spotted By: Rici Lake


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@161691 13f79535-47bb-0310-9956-ffa450edef68