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 
*  limitDescendantSize = max size of descendants any ancestor can have
     *  errString = populated with error reason if any limits are hit
     *  fSearchForParents = whether to search a tx's vin for in-mempool parents, or
     *    look up parents from mapLinks. Must be true for entries not in the mempool
     */
    bool CalculateMemPoolAncestors(const CTxMemPoolEntry& entry, setEntries& setAncestors, uint64_t limitAncestorCount, uint64_t limitAncestorSize, uint64_t limitDescendantCount, uint64_t limitDescendantSize, std::string& errString, bool fSearchForParents = true) const EXCLUSIVE_LOCKS_REQUIRED(cs);
    /** Populate setDescendants with all in-mempool descendants of hash.
     *  Assumes that setDescendants includes all in-mempool descendants of anything
     *  already in it.  */
    void CalculateDescendants(txiter it, setEntries& setDescendants) const EXCLUSIVE_LOCKS_REQUIRED(cs);
    /** The minimum fee to get into the mempool, which may itself not be enough
      *  for larger-sized transactions.
      *  The incrementalRelayFee policy variable is used to bound the time it
      *  takes the fee rate to go back down all the way to 0. When the feerate
      *  would otherwise be half of this, it is set to 0 instead.
      */
    CFeeRate GetMinFee(size_t sizelimit) const;
    /** Remove transactions from the mempool until its dynamic size is <= sizelimit.
      *  pvNoSpendsRemaining, if set, will be populated with the list of outpoints
      *  which are not in mempool which no longer have any spends in this mempool.
      */
    void TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining=nullptr);
    
    int Expire(int64_t time);
    /**
     * Calculate the ancestor and descendant count for the given transaction.
     * The counts include the transaction itself.
     */
    void GetTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants) const;
    unsigned long size() const