Core tracedb functionality. (#996)

* fixed encoding 0u8

* simplified if else stmt

* tracedb core

* more comprehensive tracedb tests

* fixed minor review issues

* addresses filter

* fixed typos

* replace malformed with corrupted

* trace switch

* db key is generic and can be made smaller

* smaller tracedb keys

* tracedb version

* fixed ignored tests

* rename Tracedb -> TraceDB

* fixed typos

* proves

* trace only top level calls to builtins to avoid DDoS attacks

* fixed tracedb config switches

* fix comments fat replaced with trace

* vector-addressing scheme for localized traces

* removed comments

* removed first, redundant 0 from trace address

* updated db.trace method

* additional tests for tracedb.trace()

ethcore/src/json_tests/executive.rs

@@ -24,6 +24,7 @@ use externalities::*;
 use substate::*;
 use tests::helpers::*;
 use ethjson;
+use trace::{Tracer, NoopTracer};
 
 #[derive(Debug, PartialEq)]
 struct CallCreate {