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

src/libstd/sync/mpsc/mod.rs

@@ -372,7 +372,7 @@ unsafe impl<T: Send> Send for Sender<T> { }
 /// The sending-half of Rust's synchronous channel type. This half can only be
 /// owned by one task, but it can be cloned to send to other tasks.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct SyncSender<T> {
+pub struct SyncSender<T: Send> {
     inner: Arc<UnsafeCell<sync::Packet<T>>>,
 }
 

src/libstd/sync/mpsc/sync.rs

@@ -47,7 +47,7 @@ use sync::mpsc::blocking::{self, WaitToken, SignalToken};
 use sync::mpsc::select::StartResult::{self, Installed, Abort};
 use sync::{Mutex, MutexGuard};
 
-pub struct Packet<T> {
+pub struct Packet<T: Send> {
     /// Only field outside of the mutex. Just done for kicks, but mainly because
     /// the other shared channel already had the code implemented
     channels: AtomicUsize,