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 
/**
 * Information about a mempool transaction.
 */
struct TxMempoolInfo
{
    
    CTransactionRef tx;
    
    int64_t nTime;
    
    CFeeRate feeRate;
    
    int64_t nFeeDelta;
};
/** Reason why a transaction was removed from the mempool,
 * this is passed to the notification signal.
 */
enum class MemPoolRemovalReason {
    UNKNOWN = 0, 
    EXPIRY,      
    SIZELIMIT,   
    REORG,       
    BLOCK,       
    CONFLICT,    
    REPLACED,    
};
class SaltedTxidHasher