relax SVN archive

Fixes for the structure.superimpose and structure.displacement user functions.

This is needed for the new atom_loop() API design.

Redesigned the model looping in the atom_loop() and base_vectors() API methods to fix a bug.

The models are now looped over in numerical order, rather than the order they were loaded or
created. This reverts to the original behaviour of the main line.

Updated the test_atom_loop_spin_selection2() unit test for the redefined atom_loop() method.

The centre_of_mass() function now averages the atomic positions over all models.

This is to fix a bug with the change to the atom_loop() API call.

Fix for the Align_tensor.test_to_and_from_xml() system test.

The domains are now defined.

The domain user function arg spin_id can now be set to None.

This is useful if the domains are not associated with spins.

Updated the scientific PDB reader atom_loop() method to match the changes to the API.

Fixes for all of the unit tests of the compile_2nd_matrix*() frame order functions.

Fix for the test_atom_loop_spin_selection2() unit test.

The atom loop is now a little different, and the position information is now always a rank-2 array.

Fix for the calls to generic_fns.align_tensor.get_tensor_index().

The arguments have been changed.