Fix issue#1082, testnet difficulty unsigned integer underflow

src/main.cpp

@@ -865,12 +865,12 @@ unsigned int static GetNextWorkRequired(const CBlockIndex* pindexLast, const CBl
     // Only change once per interval
     if ((pindexLast->nHeight+1) % nInterval != 0)
     {
-        // Special rules for testnet after 15 Feb 2012:
-        if (fTestNet && pblock->nTime > 1329264000)
+        // Special difficulty rule for testnet:
+        if (fTestNet)
         {
             // If the new block's timestamp is more than 2* 10 minutes
             // then allow mining of a min-difficulty block.
-            if (pblock->nTime - pindexLast->nTime > nTargetSpacing*2)
+            if (pblock->nTime > pindexLast->nTime + nTargetSpacing*2)
                 return nProofOfWorkLimit;
             else
             {