Tests: added "expires modified" test with proxy.
diff --git a/headers.t b/headers.t
index e3459e3..4e9c7c8 100644
--- a/headers.t
+++ b/headers.t
@@ -23,7 +23,7 @@
 select STDERR; $| = 1;
 select STDOUT; $| = 1;
 
-my $t = Test::Nginx->new()->has(qw/http/)->plan(27)
+my $t = Test::Nginx->new()->has(qw/http proxy/)->plan(28)
 	->write_file_expand('nginx.conf', <<'EOF');
 
 %%TEST_GLOBALS%%
@@ -82,6 +82,10 @@
 
         location /modified {
             expires modified 2048;
+
+            location /modified/proxy {
+                proxy_pass http://127.0.0.1:8081/modified;
+            }
         }
 
         location /var {
@@ -96,6 +100,13 @@
             }
         }
     }
+
+    server {
+        listen       127.0.0.1:8081;
+        server_name  localhost;
+
+        add_header   Last-Modified "Mon, 28 Sep 1970 06:00:00 GMT";
+    }
 }
 
 EOF
@@ -144,6 +155,16 @@
 like(http_get('/daily'), qr/Expires:.*:33 GMT/, 'expires daily');
 like(http_get('/modified'), qr/max-age=204./, 'expires modified');
 
+# "expires modified" with proxy
+
+TODO: {
+local $TODO = 'not yet' unless $t->has_version('1.13.5');
+
+like(http_get('/modified/proxy'), qr/Expires: Mon, 28 Sep 1970 06:34:08 GMT/,
+	'expires modified proxy');
+
+}
+
 # expires with variables
 
 like(http_get('/var?e=epoch'), qr/Expires:.*1970/, 'expires var epoch');