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.
