Rescale the equilibrium by setting g(psii) = gi.
   
    *NOTE* This is a rescaling in the magnetic field strength, which
    changes p and psi but leaves q invariant. Since psi is an independent
    variable in i2mex, you must make sure that subsequent interpolation
    calls use the *new* psi mesh. Therefore, it is in general a good idea
    to follow a call to i2mex_scaleG by i2mex_getOriPsi to reset the
    radial grid.
   
real(i2mex_r8), intent(in) :: psii, gi
integer, intent(out) :: ier