Vendor dependencies for 0.3.0 release

vendor/async-executor/tests/panic_prop.rs

@@ -0,0 +1,14 @@
+use async_executor::Executor;
+use futures_lite::{future, prelude::*};
+
+#[test]
+fn test_panic_propagation() {
+    let ex = Executor::new();
+    let task = ex.spawn(async { panic!("should be caught by the task") });
+
+    // Running the executor should not panic.
+    assert!(ex.try_tick());
+
+    // Polling the task should.
+    assert!(future::block_on(task.catch_unwind()).is_err());
+}