When we cache an object with a "Vary:" header, we generate
a "vary matching string" which can be used to efficiently
check for compliance when doing a cache lookup.

Only very lightly tested (ie: cnn.com).

For a full description of the reasoning, please see
	http://varnish.projects.linpro.no/wiki/ArchitectureVary



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1506 d4fa192b-c00b-0410-8231-f00ffab90ce4