Add AllowMinDifficultyBlocks chain parameter

src/miner.cpp

@@ -632,7 +632,7 @@ void static BitcoinMiner(CWallet *pwallet)
             // Update nTime every few seconds
             UpdateTime(*pblock, pindexPrev);
             nBlockTime = ByteReverse(pblock->nTime);
-            if (TestNet())
+            if (Params().AllowMinDifficultyBlocks())
             {
                 // Changing pblock->nTime can change work required on testnet:
                 nBlockBits = ByteReverse(pblock->nBits);