Revert "Remove PoW check which cannot happen anymore."
Revert "Remove PoW check which cannot happen anymore."

This reverts commit 1c92c2e9810933c9c1e1d751c60646a9866c2291.

There isn't much of a gain to remove this check so until we are 100% sure
that it's safe it'll stay.

gridcoin/Gridcoin-Research,TheCharlatan/Gridcoin-Research,caraka/gridcoinresearch,gridcoin/Gridcoin-Research,tomasbrod/Gridcoin-Research,theMarix/Gridcoin-Research,caraka/gridcoinresearch,Lederstrumpf/Gridcoin-Research,gridcoin/Gridcoin-Research,tomasbrod/Gridcoin-Research,caraka/gridcoinresearch,gridcoin/Gridcoin-Research,tomasbrod/Gridcoin-Research,TheCharlatan/Gridcoin-Research,tomasbrod/Gridcoin-Research,theMarix/Gridcoin-Research,Git-Jiro/Gridcoin-Research,Git-Jiro/Gridcoin-Research,Git-Jiro/Gridcoin-Research,Git-Jiro/Gridcoin-Research,theMarix/Gridcoin-Research,gridcoin/Gridcoin-Research,theMarix/Gridcoin-Research,theMarix/Gridcoin-Research,caraka/gridcoinresearch,Lederstrumpf/Gridcoin-Research,Lederstrumpf/Gridcoin-Research,TheCharlatan/Gridcoin-Research,gridcoin/Gridcoin-Research,Lederstrumpf/Gridcoin-Research,Lederstrumpf/Gridcoin-Research,caraka/gridcoinresearch,Lederstrumpf/Gridcoin-Research,theMarix/Gridcoin-Research,tomasbrod/Gridcoin-Research,Git-Jiro/Gridcoin-Research,TheCharlatan/Gridcoin-Research,caraka/gridcoinresearch,TheCharlatan/Gridcoin-Research