Treat the Vary response header field specially; change the
	modules that touch it to use a new routine that only adds a
	token if it isn't already present.  O(n^2) behaviour as
	Dean points out, but absent set/atom operations it seems
	a reasonable stopgap for 1.3.7.

PR:		4118 (previously closed with 'use "force-no-vary"')
Reviewed by:	Ken Coar


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83519 13f79535-47bb-0310-9956-ffa450edef68