Add a limited workaround for vary headers having double colons.

In general the "be liberal in what you accept" is a good thing, but
I am not going to be liberal about anything that could cause us to
return wrong content.

The truly consistent thing to do would be to error the fetch, but that
is a bit on the harsh-side for this specific cornercase, so I have
added a test to ignore the first character of the vary header, if it
is a colon.

Fixes:	#763



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5334 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_vary.c

@@ -82,6 +82,10 @@ VRY_Create(const struct sess *sp, const struct http *hp)
 	sbh = vsb_newauto();
 	AN(sbh);
 
+	if (*v == ':') {
+		WSP(sp, SLT_Error, "Vary header had extra ':', fix backend");
+		v++;
+	}
 	for (p = v; *p; p++) {
 
 		/* Find next header-name */