relax SVN archive

Modified InteratomContainer.id_match() to handle a single spin ID and to match to all unique IDs.

This uses the spin container _spin_ids list private metadata structure.

Small comment change.

Fixes for the J(w) mapping and consistency testing analyses for the return_interatom() changes.

Fixes for the model-free code for the return_interatom() changes.

Fix for the XML loading backwards compatibility hook for the return_interatom() changes.

Fixes for the relax 1.2 model-free results reading code for the return_interatom() changes.

Fix for the dipole_pair.define user function backend for the return_interatom() changes.

Split the return_interatom() function into two.

The new return_interatom() function is used for returning single interatomic data containers for
perfect matches, whereas the return_interatom_list() function is used to return a list of containers
matching a given spin. This simplifies the behaviour of the module.

Fixes for some of the N-state model system tests for the interatomic data design.

The RelaxNucleusError and RelaxSpinTypeError can now have the spin ID supplied.