Added some functions to specific_analyses.relax_disp.disp_data for checking if certain experiments exist.

These are the has_cpmg_exp_type() and has_r1rho_exp_type() functions.
The dispersion auto-analysis no longer references cdp.exp_type.

This follows from http://thread.gmane.org/gmane.science.nmr.relax.devel/4530, the thread about
supporting multiple data types such as SQ+MQ data simultaneously.
Fix for the dispersion auto-analysis for a bug introduced in the last commit.