- add global (multi-tile) linear solver for pair of tri-diagonal system   along X and Y lines, respectively for U and V component.   Note: 1) MPI and cube-exchange not yet coded.         2) probably not accurate for poorly conditioned / large size problem.
- add global (multi-tile) linear solver for pair of tri-diagonal system
  along X and Y lines, respectively for U and V component.
  Note: 1) MPI and cube-exchange not yet coded.
        2) probably not accurate for poorly conditioned / large size problem.

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