relax SVN archive

Restored the selection object __contains_spin_id() method as contains_spin_id().

This will allow for faster checks for matches to spin ID strings.

Fix for the pipe_control.relax_data.pack_data() function for the selection object changes.

Fixes for the cone PDB representation.

Fixes for the interatomic_loop() function for the selection object changes.

Removed the parser argument from structure.read_pdb in the stereochemistry auto-analysis.

More removals of the now dead parser argument for the structure.read_pdb user function.

Fix for the select.domain user function backend for the changes to the selection object.

Shifted the diffusion tensor structural object code to lib.structure.represent.diffusion_tensor.

The user function routes to pipe_control.structure.main.create_diff_tensor_pdb(), which pulls the
tensor info out of the data store, and then calls the diffusion_tensor() function of
lib.structure.represent.diffusion_tensor to create the representation, writes out a PDB file, and
finally adds the file to the data pipe's results file list.

Fixed some name classes in the namespace of pipe_control.structure.mass.

Shifted the cone geometric object representation functions to lib.structure.represent.cone.

The structure.create_cone_pdb user function first calls pipe_control.structure.main.create_cone_pdb()
which then calls lib.structure.represent.cone.cone(). This allows the pipe_control function to
write out the file and add it to the data pipe's results file list.