Implement the new-purge case where the entire expression comes

Implement the new-purge case where the entire expression comes
from VCL.

It is possible to instigate purges two ways from VCL now:

        sub vcl_recv {
		# Purge the req.url
                if (req.request == "PURGE") {
                        purge (req.url == req.url);
                        error 410;
                }

		# Take entire purge instruction from "Purge:" header
                if (req.request == "PURGESTR") {
                        purge ("" req.http.purge);
                        error 410;
                }

Testcase for this.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@3542 d4fa192b-c00b-0410-8231-f00ffab90ce4