Test case for issue 2718

This was already fixed by the time I read the issue, but more test
cases are always good.

Closes #2718

src/test/run-pass/issue-2718.rs

@@ -0,0 +1,38 @@
+fn sender_terminate<T:send>(p: *packet<T>) {
+}
+
+class send_packet<T: send> {
+        let mut p: option<*packet<T>>;
+        new(p: *packet<T>) { self.p = some(p); }
+        drop {
+            if self.p != none {
+                let mut p = none;
+                p <-> self.p;
+                sender_terminate(option::unwrap(p))
+            }
+        }
+        fn unwrap() -> *packet<T> {
+            let mut p = none;
+            p <-> self.p;
+            option::unwrap(p)
+        }
+}
+
+enum state {
+        empty,
+        full,
+        blocked,
+        terminated
+}
+
+type packet<T: send> = {
+        mut state: state,
+        mut blocked_task: option<task::task>,
+        mut payload: option<T>
+};
+
+fn main() {
+  let _s: send_packet<int> = send_packet(ptr::addr_of({mut state: empty,
+        mut blocked_task: none,
+        mut payload: some(42)}));
+}