Fix stream-id double-accounting bug (#112)

Both Recv::open and Rev::recv_headers check new stream ids against the
previously stream id. The second such check fails.

Now, only Recv::open performs stream id checks.

Fixes #110

tests/server.rs

@@ -22,6 +22,39 @@ fn read_preface_in_multiple_frames() {
     assert!(Stream::wait(h2).next().is_none());
 }
 
+#[test]
+fn serve_request() {
+    let _ = ::env_logger::init();
+    let (io, client) = mock::new();
+
+    let client = client
+        .assert_server_handshake()
+        .unwrap()
+        .recv_settings()
+        .send_frame(
+            frames::headers(1)
+                .request("GET", "https://example.com/")
+                .eos(),
+        )
+        .recv_frame(frames::headers(1).response(200).eos())
+        .close();
+
+    let srv = Server::handshake(io).expect("handshake").and_then(|srv| {
+        srv.into_future().unwrap().and_then(|(reqstream, srv)| {
+            let (req, mut stream) = reqstream.unwrap();
+
+            assert_eq!(req.method(), &http::Method::GET);
+
+            let rsp = http::Response::builder().status(200).body(()).unwrap();
+            stream.send_response(rsp, true).unwrap();
+
+            srv.into_future().unwrap()
+        })
+    });
+
+    srv.join(client).wait().expect("wait");
+}
+
 #[test]
 #[ignore]
 fn accept_with_pending_connections_after_socket_close() {}