Clarified hardfork comment

Author: jmjatlanta

libraries/chain/db_market.cpp

@@ -1004,7 +1004,8 @@ bool database::check_call_orders( const asset_object& mia, bool enable_black_swa
 
     const asset_bitasset_data_object& bitasset = ( bitasset_ptr ? *bitasset_ptr : mia.bitasset_data(*this) );
 
-    // previously, price feeds could cause black swan in prediction market
+    // previously, price feeds caused black swans in prediction markets
+    // happened at block 2957566, and many other times. This hardfork cannot be removed.
     if ( maint_time >= HARDFORK_CORE_460_TIME && bitasset.is_prediction_market )
        return false;