Fix the IE-identified problems with Vary (multiple instances,
	duplicate tokens) for good and all.  We can't be sure we're
	putting in all the right values for all circumstances, but
	at least now we know the field we send to the client is
	syntactically sane.  (Not that it wasn't before, but it *was*
	slightly questionable.)

PR:		4118
Submitted by:	Dean Gaudet, Roy Fielding, Ken Coar
Reviewed by:	Ken Coar


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83531 13f79535-47bb-0310-9956-ffa450edef68