Fannie Mae and Freddie Mac appear poised to make a big splash in the subprime market, thanks to tough new affordable housing goals that some analysts say will force them to buy more loans from credit-impaired borrowers on a flow basis. But those plans could be stymied by a paucity of mortgage insurance options for subprime borrowers. Indeed, a review of the earnings releases of several MIs involved in the subprime market show that