Throughout the fall, Pfizer, the maker of Viagra, has been courting Allergan, the manufacturer of Botox. Pfizer was not attracted by Allergan’s wrinkle-free face or full lips, but by its Irish “citizenship.” In its proposal to Allergan, the Viagra-maker whispered, “If we get together, we can really stiff the tax man.” In order to fulfill this goal, Pfizer would renounce …