relax SVN archive

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.

Created the generic_fns.mol_res_spin.return_molecule_by_name() function.

This will be used in the future as it is much faster than generic_fns.mol_res_spin.return_molecule()
if the molecule name is already known.

Redesign of the generic_fns.mol_res_spin.generate_spin_id() function.

The function now tries to generate a unique ID based on the spin information in the specified data
pipe. This is to attempt to fix a bug uncovered by the Structure.test_read_xyz_internal2 system
test. Defaulting in all cases to the spin name rather than spin number will often fail for a small
organic molecule, as the name in XYZ files is the atomic symbol and hence will almost never be
unique.