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.

core/state/state_test.go

@@ -72,7 +72,7 @@ func TestNull(t *testing.T) {
 	//value := common.FromHex("0x823140710bf13990e4500136726d8b55")
 	var value common.Hash
 	state.SetState(address, common.Hash{}, value)
-	state.Update()
+	state.SyncIntermediate()
 	state.Sync()
 	value = state.GetState(address, common.Hash{})
 	if !common.EmptyHash(value) {