Upgrade elastic-array to 0.9.0

This is a huge change, which includes some changes to replace code that
originally cloned to reuse allocations instead. The updated
`elastic-array` crate renames its consuming `Vec`-conversion method to
`into_vec`, which means that I can do a simple
`sed -i 's/to_vec/into_vec/'` and then fix the compilation errors.

This commit is probably a minor performance win and definitely a
significant readability win.

sync/src/api.rs

@@ -427,7 +427,7 @@ struct TxRelay(Arc<BlockChainClient>);
 impl LightHandler for TxRelay {
 	fn on_transactions(&self, ctx: &EventContext, relay: &[::ethcore::transaction::UnverifiedTransaction]) {
 		trace!(target: "pip", "Relaying {} transactions from peer {}", relay.len(), ctx.peer());
-		self.0.queue_transactions(relay.iter().map(|tx| ::rlp::encode(tx).to_vec()).collect(), ctx.peer())
+		self.0.queue_transactions(relay.iter().map(|tx| ::rlp::encode(tx).into_vec()).collect(), ctx.peer())
 	}
 }