Tue Jun 12 14:53:18 CEST 2007
Corrected misprints in 
 - (1d):
       \dot{\varphi} --> \rho^2\dot{\varphi} in two places.
 - (3'c):
       \hat{e}_1=\hat{e}_z --> \hat{e}_3=\hat{e}_z
   Thanks to Vladislav Yakovlev for noticing the misprints.