O(\alpha_s^2) contributions to the fragmentation function g_1(x,Q^2) in polarized e^+e^- annihilation

Misprints in the C_F^2 part of the splitting function \Delta P_{gq}^(1) Eq. (3.29) are corrected. Due to a minus sign error between the C_F^2- 1/2 C_A C_F piece and the remaining part of Eq. (A.4), Eq. (3.46) is changed. Finally z_{qq}^{PS,(2)} is know so that we can give the full expression for \Delta \bar {\cal C}_{1,q}^{PS} in Eq. (A.1).