change default sette options for the 4.2 branch and add warnings for options that should not be used
The branch 4.2 contains several HPC developments that are only partially coded : tiles, loop fusion and large halos.
- Their intermediate status in the 4.2 branch makes them inefficient. They should not be used by users and were only useful for the NEMO system team as an intermediate step toward the next NEMO release (5.0?).
- We were too optimistic when we fixed the default options of sette.sh and forced them to be on by default as we thought they would be efficient enough to be use in the 4.2. This is not the case and we deciced to turn them off by default as we should not use them in the 4.2. see minutes of the NST meeting of the 7th of June 2023