relax SVN archive

Improved the generic_fns.mol_res_spin.generate_spin_id_unique() function.

This can now work with molecule, residue, and spin names and numbers alternatively to the containers
supplied as arguments. For this to work, the return_molecule_by_name() function has been improved
and the functions return_residue_by_info() and return_spin_by_info() have been added.

Fix for the rdc.read user function for the recent spin ID metadata changes.

Fix for the new generate_spin_id_unique() function.

The precedence is now residue number then name, and spin name then number.

The spin_loop() function now uses generate_spin_id_unique() when the return_id flag is set.

This ensures that the caller received a unique spin ID which can be used to retrieve the
corresponding spin container.

Created the generic_fns.mol_res_spin.generate_spin_id_unique() function.

This will return a truly unique spin ID string based on the current molecule, residue, and spin data
structure.

Fixes for the metadata update of the residue and spin name and number counts.

Fix for the generic_fns.interatomic.create_interatom() function.

RelaxNoSpinWarning has been replaced with RelaxNoSpinError.

Reverted the last revision (r18737) as it was not correct and RelaxErrors should be used instead.

The command used was:
svn merge -r18737:18736 .

Missing import affecting the generic_fns.interatomic.create_interatom() function.

Bug fix for the maintenance of the spin ID lookup table metadata.

This is important for small molecules. Non-unique IDs were being placed into the lookup table,
resulting in incorrect spin containers being sometimes used. Now the molecule container has the
_res_name_count and _res_num_count metadata and the residue container the _spin_name_count and
_spin_num_count structures. These are updated via metadata_update() and are used by the
spin_id_variants() function to create a list of purely unique spin IDs.