Oxidant-Induced Hydride Abstraction from [Pt(mu-PBut2)(H)(PBut2H)]2 yielding [Pt2(mu-PBut2)2(H)(PBut2)2]X [X = C3(CN)5, TCNQ]. Spectroscopic, Crystallographic and Theoretical Comparison of the Structures of Two ``Tautomers"