(H+-K+)-ATPase inhibiting 2-[(2-pyridylmethyl)sulfinyl]benzimidazoles. 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 reactions with thiols