BOSTON — Another previously hidden perk for Massachusetts State Police troopers has been revealed.The Boston Globe reports that state officials last week released information about more than $3.4 million in additional payouts over four years, most of which went to the unit that patrols Logan International Airport, in the form of $40-per-day payouts for troopers who drive personal vehicles to work.Some troopers earned up to $13,000 each year in per diems, adding to salaries that included five- and six-figure overtime payouts.