As Auntie Mame would say, grab the maps and the martinis (we'll add "and moving boxes and packing tape"). Briggs-Freeman is opening almost 200 homes (!) this weekend, an extravaganza that will make even the most jaded house-hunter jump for joy. We're talking estates, town houses, Devonshire, Bluffview, you name it — all open for your perusal on Saturday and Sunday. Will it be the chateau on...