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/verification/verification.rs

@@ -278,8 +278,6 @@ mod tests {
 	}
 
 	impl BlockProvider for TestBlockChain {
-		fn have_tracing(&self) -> bool { false }
-
 		fn is_known(&self, hash: &H256) -> bool {
 			self.blocks.contains_key(hash)
 		}