in preparation for r*:  new S/R (calc_grad_phi_hyd.F) to compute Hydrostatic potential gradient.  pass the 2 comp. of the grad. as arguments to momentum S/R.
in preparation for r*:
 new S/R (calc_grad_phi_hyd.F) to compute Hydrostatic potential gradient.
 pass the 2 comp. of the grad. as arguments to momentum S/R.

altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h