relax SVN archive

Massive redesign of the Scientific Python structural object atom_loop() method.

The new structural data data structure is now handled, and a number of changes have occurred to the
class methods:

__molecule_loop() has been deleted.
__residue_loop() has been heavily modified.
The method __ave_atom_pos() has been added to allow the ave arg to atom_loop() to be handled.
The molecule type is stored in the molecule containers by load_pdb().

Added checks for the presence of the molecular data structures in the Scientific python structure.

The correct target molecule name structure is now passed into pack_structs() from load_pdb().

Compacted some comments.

Created the API base method target_mol_name() for generating the list of molecule names.

The load_pdb() method now creates the set_mol_name structure.

Well, a new method is required in the API base class.

Bug fix for the set up of orig_mol_num.

Removed some old, commented out code (and an old print out).

A number of bug fixes for the Scientific python structural object load_pdb() method.

The molecules are now also taken from the peptide_chains and nucleotide_chains structures, as the
molecules dictionary doesn't contain proteins or RNA!

The Scientific python structural object load_pdb() method now uses pack_structs().