Update to futures master

* Remove `LoopData` as it's no longer necessary
* Add `LoopHandle::spawn` to spawn new futures onto an event loop
* Add `LoopData::spawn` to also spawn new futures onto an event loop
* Rejigger the implementation of the event loop a bit (make a slab of futures),
  but otherwise everything else is pretty constant.

tests/spawn.rs

@@ -0,0 +1,49 @@
+extern crate tokio_core;
+extern crate env_logger;
+extern crate futures;
+
+use futures::Future;
+use tokio_core::Loop;
+
+#[test]
+fn simple() {
+    drop(env_logger::init());
+    let mut lp = Loop::new().unwrap();
+
+    let (tx1, rx1) = futures::oneshot();
+    let (tx2, rx2) = futures::oneshot();
+    lp.pin().spawn(futures::lazy(|| {
+        tx1.complete(1);
+        Ok(())
+    }));
+    lp.handle().spawn(|_| {
+        futures::lazy(|| {
+            tx2.complete(2);
+            Ok(())
+        })
+    });
+
+    assert_eq!(lp.run(rx1.join(rx2)).unwrap(), (1, 2));
+}
+
+#[test]
+fn spawn_in_poll() {
+    drop(env_logger::init());
+    let mut lp = Loop::new().unwrap();
+
+    let (tx1, rx1) = futures::oneshot();
+    let (tx2, rx2) = futures::oneshot();
+    let handle = lp.handle();
+    lp.pin().spawn(futures::lazy(move || {
+        tx1.complete(1);
+        handle.spawn(|_| {
+            futures::lazy(|| {
+                tx2.complete(2);
+                Ok(())
+            })
+        });
+        Ok(())
+    }));
+
+    assert_eq!(lp.run(rx1.join(rx2)).unwrap(), (1, 2));
+}