Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/signal_drop_signal.rs

@@ -0,0 +1,26 @@
+#![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 dropping_signal_does_not_deregister_any_other_instances() {
+    let kind = SignalKind::user_defined1();
+
+    // Signals should not starve based on ordering
+    let first_duplicate_signal = signal(kind).expect("failed to register first duplicate signal");
+    let mut sig = signal(kind).expect("failed to register signal");
+    let second_duplicate_signal = signal(kind).expect("failed to register second duplicate signal");
+
+    drop(first_duplicate_signal);
+    drop(second_duplicate_signal);
+
+    send_signal(libc::SIGUSR1);
+    let _ = sig.recv().await;
+}