relax SVN archive

Split the 'test_copy_within_molecule_fail' unit test in two, for the 2 failures.

Added a new point in the data model redesign document - the new sequence user function class.

The idea is that this is a class that handles the whole of the molecule-residue-spin structure.

Removed the spin.read(), spin.sort(), and spin.write() user function from the redesign document.

These can be implemented in a single user function class which handles molecules, residues, and
spins together.

Fixed the last of the bugs in the generic_fns.spin.copy() function.

A number of bug fixes to the spin.copy() function.

Added a test for the existence of the target residue.

Bug fix for the spin.copy() unit test 'test_copy_between_residues'.

Split the generic_fns.spin.copy() unit test 'test_copy_fail' into four unit tests.

Added another check in the spin.copy unit test 'test_copy_fail'.

Bug fixes for the spin.copy() unit test 'test_copy_between_residues'.