Arsenal have completed the signing of midfielder Fabio Vieira from Porto in a 40m euro (£34.2m) deal.   Porto released a statement on 17 June saying the Gunners would pay an initial 35m euros (£29.9m) for the 22-year-old, with the rest in potential add-ons.     Arsenal have now announced Vieira has signed a long-term contract with them.   "I am very excited that we have identified and signed such a special talent," said Gunners boss Mikel Arteta.   "Fabio is a very creative player that will bring high quality and versatility to our attacking play."   Vieira has yet