Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/signal_drop_recv.rs

@@ -0,0 +1,22 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+#![cfg(unix)]
+
+mod support {
+    pub mod signal;
+}
+use support::signal::send_signal;
+
+use tokio::signal::unix::{signal, SignalKind};
+
+#[tokio::test]
+async fn drop_then_get_a_signal() {
+    let kind = SignalKind::user_defined1();
+    let sig = signal(kind).expect("failed to create first signal");
+    drop(sig);
+
+    send_signal(libc::SIGUSR1);
+    let mut sig = signal(kind).expect("failed to create second signal");
+
+    let _ = sig.recv().await;
+}