future queued block support

- queued       bool // flag for blockpool to skip TD check
- set to true when future block queued
- in checkTD: skip check if queued
- TODO: add test (insertchain sets future block)

core/chain_manager.go

@@ -471,6 +471,7 @@ func (self *ChainManager) InsertChain(chain types.Blocks) error {
 			// Do not penelise on future block. We'll need a block queue eventually that will queue
 			// future block for future use
 			if err == BlockFutureErr {
+				block.SetQueued(true)
 				self.futureBlocks.Push(block)
 				stats.queued++
 				continue