JSON transaction parser: detect file-order stream and disable the early termination...

the early termination logic is useful when transactions come in reverse
chronological order -- newest first. seeing 50 known transactions
seems like a good criteria for terminating the parsing before the whole
stream is processed

however, the JSON API seems to return transactions in file order --
oldest first (by time of creation, not 'date' field). in this order
the newest (and thus unknown) transactions come last and the early
termination logic needs to be disabled