relax SVN archive

This redesign is required due to problems encountered by Han in the xyz branch. See the thread
starting at https://mail.gna.org/public/relax-devel/2011-07/msg00021.html.

This commit consists of a number of changes:
- The combine_models argument has been removed as it is a relic, and isn't used at all.
- The spins are now created in the standard way via the generic_fns.mol_res_spin.create_spin()
function, eliminating all of the issues and complications of the old code.
- The atomic positions are now converted to numpy arrays.
- Only the created spins are included in the print out, and not replicated for each model.