[PoS] StakeV1: iterate the time backwards.
[PoS] StakeV1: iterate the time backwards.

makes the miner more efficient, reducing the amount of kernels re-hashed
between successive runs.
Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,Mrs-X/PIVX,Mrs-X/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX