Don't block sync when importing old blocks (#8530)

* Alter IO queueing.

* Don't require IoMessages to be Clone

* Ancient blocks imported via IoChannel.

* Get rid of private transactions io message.

* Get rid of deadlock and fix disconnected handler.

* Revert to old disconnect condition.

* Fix tests.

* Fix deadlock.

ethcore/sync/src/lib.rs

@@ -54,6 +54,8 @@ extern crate macros;
 extern crate log;
 #[macro_use]
 extern crate heapsize;
+#[macro_use]
+extern crate trace_time;
 
 mod chain;
 mod blocks;