(H+-K+)-ATPase Inhibiting 2-((2-Pyridylmethyl)sulfinyl)benzimidazoles. Part 2. The Reaction Cascade Induced by Treatment with Acids. Formation of 5H-Pyrido(1′,2′:4,5)(1,2,4)thiadiazino(2,3-a)benzimidazol-13-ium Salts and Their Reactio