Added k_AB to parameters.

Progress sr #3071: https://gna.org/support/index.php?3071 - Implementation of Tollinger/Kay dispersion model (2001)
Following the guide at: http://wiki.nmr-relax.com/Tutorial_for_adding_relaxation_dispersion_models_to_relax

Troels E. Linnet provided this patch. Commit by: tlinnet _aaattt_ gmail_dot_com

Signed-off-by: Edward d'Auvergne <edward@nmr-relax.com>
More fixes for the relax_disp.exp_type user function changes.
Merged revisions 20912 via svnmerge from 
svn+ssh://bugman@svn.gna.org/svn/relax/trunk

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  r20912 | bugman | 2013-09-06 17:27:22 +0200 (Fri, 06 Sep 2013) | 3 lines
  
  Removed a debugging printout.
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Removed some debugging printouts fatal for Python3.