Turned off the optimisation constraints for the 'R2eff' model in the dispersion auto-analysis.
This follows from http://thread.gmane.org/gmane.science.nmr.relax.scm/22977/focus=6829.
This model does not require constraints at all, and the constraints only cause the optimisation to
take 10x longer to complete. Therefore the constraint flag has been set to False for the model.
