limitfreerelay edge case bugfix:

If a new transaction will cause limitfreerelay
to be exceeded it should not be accepted
into the memory pool and the byte counter
should be updated only after the fact.

src/main.cpp

@@ -1016,7 +1016,7 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState &state, const C
             nLastTime = nNow;
             // -limitfreerelay unit is thousand-bytes-per-minute
             // At default rate it would take over a month to fill 1GB
-            if (dFreeCount >= GetArg("-limitfreerelay", DEFAULT_LIMITFREERELAY) * 10 * 1000)
+            if (dFreeCount + nSize >= GetArg("-limitfreerelay", DEFAULT_LIMITFREERELAY) * 10 * 1000)
                 return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "rate limited free transaction");
             LogPrint("mempool", "Rate limit dFreeCount: %g => %g\n", dFreeCount, dFreeCount+nSize);
             dFreeCount += nSize;