Rewrote the logic of the key-word 'optimise_r2eff' in the auto analyses of relax disp.
If R2eff result file exist in the 'pre_run_dir', this is loaded.
If the results contain both values, and errors, then no optimisation is performed on the R2eff model.
Unless the 'optimise_r2eff' flag is raised, which is not standard.
