tx pool: don't drop cxns relaying key images spent in chain

Author: j-berman

src/cryptonote_core/blockchain.cpp

@@ -3855,7 +3855,7 @@ bool Blockchain::check_tx_inputs(transaction& tx,
 
     if(have_tx_keyimg_as_spent(in_to_key.k_image))
     {
-      MERROR_VER("Key image already spent in blockchain: " << epee::string_tools::pod_to_hex(in_to_key.k_image));
+      MERROR_VER("Key image already spent in blockchain: " << epee::string_tools::pod_to_hex(in_to_key.k_image) << " of tx " << get_transaction_hash(tx));
       tvc.m_double_spend = true;
       return false;
     }

src/cryptonote_core/tx_pool.cpp

@@ -273,6 +273,8 @@ namespace cryptonote
         LOG_PRINT_L1("tx used wrong inputs, rejected");
         tvc.m_verifivation_failed = true;
         tvc.m_invalid_input = true;
+        if (tvc.m_double_spend)
+          tvc.m_no_drop_offense = true;
         return false;
       }
     }else