Only keep setBlockIndexValid entries that are possible improvements
Only keep setBlockIndexValid entries that are possible improvements

(cherry picked from commit 714a3e6505d986d064d3a34038a724ac1cad5308)

reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin