Updated 4DVar surface forcing adjustment

[arango]

The 4DVar adjustment of surface forcing (ADJUST_WSTRESS and ADJUST_STFLUX) was revisited in view of the new IS4DVAR algorithm with preconditioning. To avoid confussion, the surface fluxes in output tangent linead and adjoint NetCDF files are written as kinematic fluxes (m2/s2 for stress and Celsius m/s heat flux). However, the same variables associated with the nonlinear model are scaled to Pa and W/m2, respectively.

Additional logic is added when the surface forcing is computed using the BULK_FLUXES option. In this case, the fields are convolved since the minimization is done in v-space.

The bacground cost function term (Jb) was corrected to add contributions from all previous outer loops.

Many thanks to Andy Moore for looking and testing this option in the new IS4DVAR algorithm.