Influence of Drug Binding on DNA Hydration: Acoustic and Densimetric Characterizations of Netropsin Binding to the Poly(dAdT).cntdot.Poly(dAdT) and Poly(dA).cntdot.Poly(dT) Duplexes and the Poly(dT).cntdot.Poly(dA).cntdot.Poly(dT) Triplex at 25 .degree.C