Modified sponge parameters ICOLMDZ to use same treatment as LMDZ (iflag_sponge=2, mode_sponge=3).
Remind :
iflag_sponge !0 --> for no sponge
!1 --> for sponge over 4 topmost layers
!2 --> for sponge from top to ~1% of top layer pressure
mode_sponge !1 --> u and v relax towards 0
!2 --> u and v relax towards their zonal mean
!3 --> u,v and pot. temp. relax towards their zonal mean