Added support for the 'TP02' model to the relax_disp.select_model user function back end.
This is the Trott and Palmer 2002 R1rho analytic model for 2-site exchange.
This commit follows step 6 of the relaxation dispersion model addition tutorial (http://thread.gmane.org/gmane.science.nmr.relax.devel/3907).
Authored by: bugman 2013-07-31
Parent: [r20492]
Child: [r20494]
