Better management of the global relaxation dispersion data.
The user functions relax_disp.cpmg_frq, relax_disp.spin_lock_nu1, and relax_disp.relax_time now
maintain data structures in the current data pipe of the unique frequencies, fields, and times
(sorted) as well as the number of frequencies, fields, and times. This data is used by the minimise
user function back end to set up the target function, and will be required by many other parts of
the analysis.
