Transaction eras (#758)

* Initial groundwork

* A mess.

* Integrate

* Fix tests

* Unit tests

* Tests for unchecked_extrisnic

* fix tab

* Improve binary format.

* fix tests

* Rename extrinsic-pool -> transaction-pool

Closes #770

* Implement unimplemented.

* typo

substrate/core/transaction-pool/src/error.rs

@@ -0,0 +1,33 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! External Error trait for extrinsic pool.
+
+use txpool;
+
+/// Extrinsic pool error.
+pub trait IntoPoolError: ::std::error::Error + Send + Sized {
+	/// Try to extract original `txpool::Error`
+	///
+	/// This implementation is optional and used only to
+	/// provide more descriptive error messages for end users
+	/// of RPC API.
+	fn into_pool_error(self) -> Result<txpool::Error, Self> { Err(self) }
+}
+
+impl IntoPoolError for txpool::Error {
+	fn into_pool_error(self) -> Result<txpool::Error, Self> { Ok(self) }
+}