relax SVN archive

Try that fix again!

Fix for the test_atom_loop_spin_selection2() unit test.

Fix for the atom_loop() method needed because of the load_pdb() changes.

Fix for the test_load_pdb() unit test.

Fixed some references to os.path.

Added the missing struct_index to load_pdb().

Redesigned the internal and Scientific load_pdb() methods.

An auxiliary method __add_struct() was created for looking after the structure additions.

Added the NMR model number to the collection of structural attributes stored as lists.

The load_pdb() structural method now accepts the struct_index arg.

This is passed in by from_xml() to place the structure in the correct position.

Modified from_xml() to handle multiple loaded structures.