Handle Cache-control: (private|no-cache|no-store) by default

As per discussion at the Varnish dev meeting, seeing Cache-control:
no-cache (and friends) now disable caching by default.  As a twist, we
respect Surrogate-control if that is present, in the default VCL.

Fixes: 1124
References: 477

bin/varnishd/default.vcl

@@ -104,6 +104,9 @@ sub vcl_miss {
 sub vcl_fetch {
     if (beresp.ttl <= 0s ||
         beresp.http.Set-Cookie ||
+        beresp.http.Surrogate-control ~ "no-store" ||
+        (!beresp.http.Surrogate-Control &&
+          beresp.http.Cache-Control ~ "no-cache|no-store|private") ||
         beresp.http.Vary == "*") {
 		/*
 		 * Mark as "Hit-For-Pass" for the next 2 minutes