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.

ethcore/src/miner/stratum.rs

@@ -145,7 +145,7 @@ impl JobDispatcher for StratumJobDispatcher {
 		);
 
 		self.with_core_void(|client, miner| {
-			let seal = vec![encode(&payload.mix_hash).to_vec(), encode(&payload.nonce).to_vec()];
+			let seal = vec![encode(&payload.mix_hash).into_vec(), encode(&payload.nonce).into_vec()];
 			if let Err(e) = miner.submit_seal(&*client, payload.pow_hash, seal) {
 				warn!(target: "stratum", "submit_seal error: {:?}", e);
 			};