Developer Martin Ginsburg sees a better market for rentals than condominiums, at least right now, in Haverstraw and has decided to offer rentals in his project The Waterfront at Harbors. Part of Valhalla-based Ginsburg Development Cos.’ larger Harbors-at-Haverstraw community, the 40-units in The Waterfront at Harbors originally were going to be marketed as condos starting…