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/light/src/net/tests/mod.rs

@@ -137,7 +137,7 @@ impl Provider for TestProvider {
 
 	fn storage_proof(&self, req: request::CompleteStorageRequest) -> Option<request::StorageResponse> {
 		Some(StorageResponse {
-			proof: vec![::rlp::encode(&req.key_hash).to_vec()],
+			proof: vec![::rlp::encode(&req.key_hash).into_vec()],
 			value: req.key_hash | req.address_hash,
 		})
 	}