Derive IPC interface only when ipc feature is on (#2463)

* derive -> ipc

* accident repair

* conditional ipc deriving

* fix test

ethcore/src/tests/mod.rs

@@ -16,4 +16,5 @@
 
 pub mod helpers;
 mod client;
+#[cfg(feature="ipc")]
 mod rpc;

ethcore/src/tests/rpc.rs

@@ -19,7 +19,8 @@
 use nanoipc;
 use std::sync::Arc;
 use std::sync::atomic::{Ordering, AtomicBool};
-use client::{Client, BlockChainClient, ClientConfig, RemoteClient, BlockID};
+use client::{Client, BlockChainClient, ClientConfig, BlockID};
+use client::remote::RemoteClient;
 use tests::helpers::*;
 use devtools::*;
 use miner::Miner;