Few dealers in town can claim the longevity of Barbara Gillman, who began peddling art out of her home 40 years ago. "Back then I was selling to local banks and thought, 'Wow! This is easy.'"The self-styled doyenne of the fledgling South Florida arts scene went on to open her own gallery in 1979 and quickly began inviting monster names to the Big Orange at a time when local collectors were a rare breed."I brought Andy Warhol here in 1980 and James Rosenquist in 1982," Gillman says. When she conv