Fix for all edge case 'no Rex' failures of the 'NS CPMG 2-site expanded' model.
This uses the no exchange checking idea, modified to function in the relax trunk, from
http://article.gmane.org/gmane.science.nmr.relax.devel/5847. This is importantly on line 1 of the
function.
The recently introduced set of 7 unit tests (r23327) comprehensively showing these failures now all
pass. This commit is mainly for demonstration purposes.
