Allergan Inc., the maker of wrinkle-smoothing Botox, has agreed to pay $600 million to settle a yearslong federal investigation into its marketing of the top-selling, botulin-based drug.The Justice Department and the company said Wednesday in a statement it will plead guilty to one misdemeanor charge of "misbranding," in which the company's marketing led physicians to use Botox for unapproved uses. Those included the treatment of headache, pain, spasticity and cerebral palsy in children.