Major updates integration from all upstreams

src/consensus/params.h

@@ -23,6 +23,7 @@ enum UpgradeIndex {
     BASE_SPROUT,
     UPGRADE_TESTDUMMY,
     UPGRADE_OVERWINTER,
+    UPGRADE_SAPLING,
     // NOTE: Also add new upgrades to NetworkUpgradeInfo in upgrades.cpp
     MAX_NETWORK_UPGRADES
 };
@@ -111,6 +112,7 @@ struct Params {
     int64_t AveragingWindowTimespan() const { return nPowAveragingWindow * nPowTargetSpacing; }
     int64_t MinActualTimespan() const { return (AveragingWindowTimespan() * (100 - nPowMaxAdjustUp  )) / 100; }
     int64_t MaxActualTimespan() const { return (AveragingWindowTimespan() * (100 + nPowMaxAdjustDown)) / 100; }
+    uint256 nMinimumChainWork;
 };
 } // namespace Consensus