Removed the variable 'C_module_exp_fn' from __builtin__.
See the thread starting at https://mail.gna.org/public/relax-devel/2007-02/msg00003.html
(Message-id: <45DACFEA.7020108@...>) for a discussion of the issue.
Rathar than placing the 'C_module_exp_fn' variable into __builtin__ from the specific_fns.relax_fit
module, it is now placed into the global namespace of that module. The generic_fns.runs module then
simply imports the variable.
