Added T:Send bound to Queue<T> to avoid specialized Drop impl.

src/libstd/sync/mpsc/mpsc_queue.rs

@@ -72,7 +72,7 @@ struct Node<T> {
 /// The multi-producer single-consumer structure. This is not cloneable, but it
 /// may be safely shared so long as it is guaranteed that there is only one
 /// popper at a time (many pushers are allowed).
-pub struct Queue<T> {
+pub struct Queue<T: Send> {
     head: AtomicPtr<Node<T>>,
     tail: UnsafeCell<*mut Node<T>>,
 }

src/libstd/sync/mpsc/shared.rs

@@ -40,7 +40,7 @@ const MAX_STEALS: isize = 5;
 #[cfg(not(test))]
 const MAX_STEALS: isize = 1 << 20;
 
-pub struct Packet<T> {
+pub struct Packet<T: Send> {
     queue: mpsc::Queue<T>,
     cnt: AtomicIsize, // How many items are on this channel
     steals: isize, // How many times has a port received without blocking?