Added unit test for return_offset_data.
Regarding sr #3124, (https://gna.org/support/index.php?3124) - Grace graphs production for R1rho analysis with R2_eff as function of Omega_eff.
This is development according to thread http://thread.gmane.org/gmane.science.nmr.relax.devel/5157.
Authored by: tlinnet 2014-03-06
Parent: [r22413]
Child: [r22415]
