relax SVN archive

Updated the Structure.test_displacement_molecules system test.

This is for the changes to the structure.displacement user function.

Another refinement for the structure ID strings returned by the assemble_coord_array() function.

Converted the structure.displacement user function to the new pipes/models/molecules/atom_id design.

This allows the displacements to be calculated between atomic coordinates from different data pipes,
different structural models, and different molecules. The user function backend has been hugely
simplified as it now uses the new pipe_control.structure.main.assemble_coordinates() function.

The Structure.test_displacement system test has been updated for the user function argument changes.

Converted the internal structural displacement object to use unique IDs rather than model numbers.

This allows the object to be much more flexible in what types of structures it can handle. This is
in preparation for a change in the structure.displacement user function.

More improvements for the structure ID strings returned by the assemble_coord_array() function.

More improvements for the structure ID strings returned by the assemble_coord_array() function.

Changed the structure ID strings returned by the assemble_coord_array() function.

This is from the lib.structure.internal.coordinates module. The structural object name is only
included if more than one structural object has been supplied.

The coordinate assembly function now returns list of unique IDs.

This is for each structural object, model and molecule.

Comment fix.

Tooltip standardisation for the structure.align and structure.find_pivot user functions.