util reexports less std

ethcore/src/client/test_client.rs

@@ -17,6 +17,8 @@
 //! Test client.
 
 use std::sync::atomic::{AtomicUsize, Ordering as AtomicOrder};
+use std::collections::{HashMap, BTreeMap};
+use std::mem;
 use rustc_hex::FromHex;
 use util::*;
 use rlp::*;