relax SVN archive

Fixes for the centre of mass function.

Bug fix for the atom_loop() API generator method.

Wrote the atom_loop() API function for the Scientific Python PDB structure object.

The centre of mass function now works if the sequence does not exist in the current data pipe.

The spin_num and spin_name have been renamed to atom_num and atom_name respectively in the function
as well.

Modified centre_of_mass() to call a new generator function atom_loop() in the structural data object.

Added a missing import.

Fixed a test for the presence of structural data in the current data pipe.

Fixed the call to the centre_of_mass() function in the N-state model code.

Removed a broken and now useless test.

An initial print out for the parser type.