This is to track the regression introduced in master, which needs fixing for 0.14. See #9240, #9371, etc.
UNKNOWN = 0, 
    EXPIRY,      
    SIZELIMIT,   
    REORG,       
    BLOCK,       
    CONFLICT,    
    REPLACED     
};
/**
 * CTxMemPool stores valid-according-to-the-current-best-chain transactions
 * that may be included in the next block.
 *
 * Transactions are added when they are seen on the network (or created by the
 * local node), but not all transactions seen are added to the pool. For
 * example, the following new transactions will not be added to the mempool:
 * - a transaction which doesn't make the mimimum fee requirements.
 * - a new transaction that double-spends an input of a transaction already in
 * the pool where the new transaction does not meet the Replace-By-Fee
 * requirements as defined in BIP 125.
 * - a non-standard transaction.
 *
 * CTxMemPool::mapTx, and CTxMemPoolEntry bookkeeping:
 *
 * mapTx is a boost::multi_index that sorts the mempool on 4 criteria:
 * - transaction hash
 * - feerate [we use max(feerate of tx, feerate of tx with all descendants)]
 * - time in mempool
 * - mining score (feerate modified by any fee deltas from PrioritiseTransaction)
 *