Fix for the y-axis in the per spin dispersion curve plots.
This fix follows from the thread http://thread.gmane.org/gmane.science.nmr.relax.devel/4512.
The test for CPMG-type data was incorrect and should use the CPMG_EXP variable.
Authored by: bugman 2013-09-04
Parent: [r20795]
Child: [r20797]
