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

* derive -> ipc

* accident repair

* conditional ipc deriving

* fix test

sync/build.rs

@@ -17,5 +17,5 @@
 extern crate ethcore_ipc_codegen;
 
 fn main() {
-	ethcore_ipc_codegen::derive_ipc("src/api.rs").unwrap();
+	ethcore_ipc_codegen::derive_ipc_cond("src/api.rs", cfg!(feature="ipc")).unwrap();
 }

sync/src/lib.rs

@@ -63,3 +63,9 @@ pub use api::{EthSync, SyncProvider, SyncClient, NetworkManagerClient, ManageNet
 	ServiceConfiguration, NetworkConfiguration};
 pub use chain::{SyncStatus, SyncState};
 pub use network::{is_valid_node_url, NonReservedPeerMode, NetworkError};
+
+/// IPC interfaces
+#[cfg(feature="ipc")]
+pub mod remote {
+	pub use api::{SyncClient, NetworkManagerClient};
+}