Bugfix: I forgot to divide by sin(ThetaW) when calculating the counterterm
'delta sin(ThetaW)'.  Note: Denner Eq. (4.5.45) says

  delta sin(ThetaW)^2 = - cos(ThetaW)^2 Re(... - ...)

  delta sin(ThetaW) = delta sin(ThetaW)^2 / (2 sin(ThetaW))

=>

  delta sin(ThetaW) = - 0.5 cos(ThetaW)^2 Re(... - ...) / sin(ThetaW)