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.

miner/worker.go

@@ -453,7 +453,7 @@ func (self *worker) commitNewWork() {
 	if atomic.LoadInt32(&self.mining) == 1 {
 		// commit state root after all state transitions.
 		core.AccumulateRewards(self.current.state, header, uncles)
-		current.state.Update()
+		current.state.SyncObjects()
 		self.current.state.Sync()
 		header.Root = current.state.Root()
 	}