“This court must not only not give credence to the father’s manifestly irrational and patently absurd view of the French judiciary: it must not assume that the French judge will refuse such a request, let alone that he or she will not deal with it fairly and appropriately. Indeed, the only legitimate assumption which the court can and, and indeed, must make about the exercise of its judicial powers by a co-signatory under the Hague Convention and Brussels II Revised is that the court in the foreign state, since it is seized with the question of [P]’s welfare, will exercise its powers properly and fairly and will reach an appropriate decision which it deems to be in the best interest of [P].”