Limiting result of the execution to execution-specific errors (#1071)

* execution error/result limiting

* missing trailing comma

* fix executive tests

* adding original error as string to the generic transaction error

* 'mallformed'-s all around

ethcore/src/error.rs

@@ -59,7 +59,9 @@ pub enum ExecutionError {
 		got: U512
 	},
 	/// Returned when internal evm error occurs.
-	Internal
+	Internal,
+	/// Returned when generic transaction occurs
+	TransactionMalformed(String),
 }
 
 #[derive(Debug, PartialEq)]