Move ethcore::Error to error_chain (#8386)

* WIP

* Convert Ethcore error to use error_chain

* Use error_chain for ImportError and BlockImportError

* Fix error pattern matches for error_chain in miner

* Implement explicit From for AccountsError

* Fix pattern matches for ErrorKinds

* Handle ethcore error_chain in light client

* Explicitly define Result type to avoid shadowing

* Fix remaining Error pattern matches

* Fix tab space formatting

* Helps if the tests compile

* Fix error chain matching after merge

ethcore/src/executed.rs

@@ -24,7 +24,7 @@ use trace::{VMTrace, FlatTrace};
 use log_entry::LogEntry;
 use state_diff::StateDiff;
 
-use std::fmt;
+use std::{fmt, error};
 
 /// Transaction execution receipt.
 #[derive(Debug, PartialEq, Clone)]
@@ -148,6 +148,12 @@ impl fmt::Display for ExecutionError {
 	}
 }
 
+impl error::Error for ExecutionError {
+	fn description(&self) -> &str {
+		"Transaction execution error"
+	}
+}
+
 /// Result of executing the transaction.
 #[derive(PartialEq, Debug, Clone)]
 pub enum CallError {