improved land-processor suppression

[smasson]

Context

Today, land-processor are suppressed only if they are completely in a land.
I think, since the recent modifications in mppini, we could suppress domains, which have only their internal area (from nldi/j to nlei/j) in land.
This append for example with ORCA2 with a 7x4 decomposition. Today we must put jpnij = 27, we should be able to put 26.

Proposal

replace in mppini.F90

         !
         ! Check wet points over the entire domain to preserve the MPI communication stencil
         isurf = 0
         DO jj = 1, ilj
            DO  ji = 1, ili

by

         !
         ! Check wet points over the internal domain as MPI communication stencil will be latter modified in case of domain suppression
         isurf = 0
         DO jj = ildj(ii,ij), ilej(ii,ij)
            DO  ji = ildi(ii,ij), ilei(ii,ij)

[smasson]

In fact we have to be careful with the corners...
As we do east-west communications first and next north-south communications, the corner values are obtained through the north-south exchanges.
We therefore have to take care of the northern and southern neighbors of the land-domain we want to suppress. The corner values of these neighbors won't be received anymore, so we have to make sure they are land points. These corners points are also existing on the overlapping bands of the land-domain we want to suppress, their position is

• For the northern neighbor: (1, jpj-1) and (jpi, jpj-1), that must be land
• For the southern neighbor: (1, 2) and (jpi, 2), that must be land

So to suppress a land-domain, we have to make sure its internal area and these 4 points (if this domain has norther and/or southern neighbors) are land-points.