Bugfix: When comparing current block, only pay attention to the prevblock header

Formerly, it included the version, which might not always be the same between pools

cgminer.c

@@ -2558,7 +2558,7 @@ static void test_work_current(struct work *work)
 
 	uint32_t block_id = ((uint32_t*)(work->data))[1];
 
-	hexstr = bin2hex(work->data, 18);
+	hexstr = bin2hex(&work->data[4], 18);
 	if (unlikely(!hexstr)) {
 		applog(LOG_ERR, "stage_thread OOM");
 		return;