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/client/header_chain.rs

@@ -388,7 +388,7 @@ impl HeaderChain {
 				None => {
 					match self.db.get(self.col, &hash) {
 						Ok(db_value) => {
-							db_value.map(|x| x.to_vec()).map(encoded::Header::new)
+							db_value.map(|x| x.into_vec()).map(encoded::Header::new)
 								.and_then(|header| {
 									cache.insert_block_header(hash.clone(), header.clone());
 									Some(header)