core, miner, tests: renamed state methods

* Update => SyncIntermediate
* Added SyncObjects

SyncIntermediate only updates whatever has changed, but, as a side
effect, requires much more disk space.

SyncObjects will only sync whatever is required for a block and will not
save intermediate state to disk. As drawback this requires more time
when more txs come in.

tests/state_test_util.go

@@ -175,7 +175,7 @@ func RunState(statedb *state.StateDB, env, tx map[string]string) ([]byte, state.
 	if core.IsNonceErr(err) || core.IsInvalidTxErr(err) || state.IsGasLimitErr(err) {
 		statedb.Set(snapshot)
 	}
-	statedb.Update()
+	statedb.SyncObjects()
 
 	return ret, vmenv.state.Logs(), vmenv.Gas, err
 }