Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
{
        
        
        double f1 = (double)a.GetModifiedFee() * a.GetSizeWithDescendants();
        double f2 = (double)a.GetModFeesWithDescendants() * a.GetTxSize();
        if (f2 > f1) {
            mod_fee = a.GetModFeesWithDescendants();
            size = a.GetSizeWithDescendants();
        } else {
            mod_fee = a.GetModifiedFee();
            size = a.GetTxSize();
        }
    }
};
/** \class CompareTxMemPoolEntryByScore
 *
 *  Sort by feerate of entry (fee/size) in descending order
 *  This is only used for transaction relay, so we use GetFee()
 *  instead of GetModifiedFee() to avoid leaking prioritization
 *  information via the sort order.
 */
class CompareTxMemPoolEntryByScore