ap_expr: Add req_novary function that allows HTTP header lookups

without adding the name to the Vary header.

Submitted by: sf
Backported by: rjung
Reviewed by: rjung, jailletc36, sf

Backport of r1403483 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1422586 13f79535-47bb-0310-9956-ffa450edef68