Conflicts:
	bin/varnishd/cache/cache_vcl.c
	bin/varnishd/cache/cache_vcl.h
	bin/varnishd/cache/cache_vrt_filter.c

It was possible to back-port this change without bringing beresp.filters
and changing the VRT interface. So we get the benefits of this change
and more that will follow and leave the possibility to minor-bump VRT to
back-port beresp.filters in the future if that doesn't break.

This clearly breaks $ABI strict VMODs, but that's part of the deal.