relax SVN archive

The pcs.read user function backend now uses generic_fns.mol_res_spin.generate_spin_id_unique().

This allows the matching spin container to always be returned for storing the data.

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.