Fannie Mae and Freddie Mac are primed to remain active buyers in the subprime mortgage securities market after federal regulators this week pushed through a new rule instituting tough new affordable-housing goals for the government-sponsored enterprises. The Department of Housing and Urban Development announced this week that it would continue to hold Fannie’s and Freddie’s feet to the fire in order to compel the two firms to lead the market in support of underserved borrowers.…