relax SVN archive

Fix for the test_load_structures() unit test.

Shifted the 'test.pdb' file into the directory for data shared between the system and unit tests.

Added the framework for the unit tests of the Scietific Python PDB structural object.

Included is a test of the load_structures() method.

Added the _structure directory to the __all__ list.

Added the directory for the unit tests of the generic_fns.structure package.

Docstring fix for the __residue_loop() method.

Started an implementation of Selection.__contains_spin_id().

Split up the Selection.__contains__() method to allow for string comparisons as well.

The MoleculeContainer, ResidueContainer, and/or SpinContainer comparison has been shifted to the
method Selection.__contains_mol_res_spin_containers().

Improved the test_Selection_full_spin_id() unit test to test all spins.

Removed the heteronuc arg test of the structure.vectors() user function.

This argument is no longer present.