relax SVN archive

Bug fix in the load_spins() function.

Renamed incorrectly named variables.

Modified load_spins() to handle a single molecule with no name.

Added some missing imports.

Buf fix for the system test for the loading of a sequence from a PDB file.

The N atom was incorrectly specified.

Added the atom_id keyword to the Scientific Python PDB data object atom_loop() method.

Fixes and expansion of the system test for the loading of a sequence from a PDB file.

Removed the import of the now non-existant generic_fns.sequence.load_PDB_sequence() function.

Completion of generic_fns.structure.main.load_spins() and allowed atom selections in atom_loop().

The generic_fns.structure.main.load_spins() function now uses the structural data object API method
atom_loop() to generate the molecule, residue, and spin sequence in the relax data store. The
sequence generation code is mainly from the old load_PDB_sequence() function.

The Scientific Python data object atom_loop() generator method has been updated to allow for only
selected atoms to be yielded.

Merged generic_fns.sequence.load_PDB_sequence() into generic_fns.structure.main.load_spins().

Removed the call to load_PDB_sequence().

The main part of load_PDB_sequence() will shifted to this load_spins() function. Those parts
specific to the Scientific Python PDB representation will be shifted to the atom_loop() method of
the new scientific python data object.