“… an investment fund pooling the assets of a retirement pension scheme is not a ‘special investment fund’ within the meaning of those provisions, management of which may be exempted from value added tax in the light of the objective of those directives and the principle of fiscal neutrality, where the members of the scheme do not bear the risk arising from the management of the fund and the contributions which the employer pays into the scheme are a means by which he complies with his legal obligations towards his employees.”