vtc: Import r03564 from the 6.0 branch

Refs 31e3895a

bin/varnishtest/tests/r03564.vtc

+varnishtest "sess.* symbols and vcl syntax"
+
+varnish v1 -vcl {
+	backend be none;
+
+	sub vcl_deliver {
+		set resp.http.sess-xid = sess.xid;
+		set resp.http.sess-timeout-idle = sess.timeout_idle;
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.http.sess-xid == 1000
+	expect resp.http.sess-timeout-idle == 5.000
+} -run
+
+varnish v1 -syntax 4.0 -vcl {
+	backend be none;
+	sub vcl_deliver {
+		set resp.http.sess-timeout-idle = sess.timeout_idle;
+	}
+}
+
+varnish v1 -syntax 4.0 -errvcl "Symbol not found: 'sess.xid'" {
+	backend be none;
+	sub vcl_deliver {
+		set resp.http.sess-xid = sess.xid;
+	}
+}