Store CX receipts in blocks in CrossTxEpoch

Previously, CX receipt storage started at CrossTxEpoch+1, causing
incoming CX receipts in blocks in CrossTxEpoch to be lost.

core/blockchain.go

@@ -1102,7 +1102,7 @@ func (bc *BlockChain) WriteBlockWithState(
 
 	//// Cross-shard txns
 	epoch := block.Header().Epoch()
-	if bc.chainConfig.AcceptsCrossTx(block.Epoch()) {
+	if bc.chainConfig.HasCrossTxFields(block.Epoch()) {
 		shardingConfig := shard.Schedule.InstanceForEpoch(epoch)
 		shardNum := int(shardingConfig.NumShards())
 		for i := 0; i < shardNum; i++ {