Started to implement the relaxation dispersion analysis specific calculate() method.
This will be used to calculate the R2eff/R1rho values for the fixed relaxation time period data types
and is equivalent to Sebastien Morin's relax_disp.calc_r2eff user function deleted at r19580
(see http://thread.gmane.org/gmane.science.nmr.relax.scm/17336).
