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/client/client.rs

@@ -1443,7 +1443,7 @@ impl BlockChainClient for Client {
 	}
 
 	fn block_receipts(&self, hash: &H256) -> Option<Bytes> {
-		self.chain.read().block_receipts(hash).map(|receipts| ::rlp::encode(&receipts).to_vec())
+		self.chain.read().block_receipts(hash).map(|receipts| ::rlp::encode(&receipts).into_vec())
 	}
 
 	fn import_block(&self, bytes: Bytes) -> Result<H256, BlockImportError> {