relax SVN archive

Fixed the call to generate_spin_id() in the return_spin_from_index() function.

Renamed generate_spin_id() to generate_spin_id_data_array(), and created a new generate_spin_id().

The generate_spin_id_data_array() function generates the spin_id string from a data array whereas
generate_spin_id() generates the spin_id string from the argument values passed into it.

Added the structural API atom_loop() call to the vectors() function.

Renamed the structural API base class method num_str() to num_models().

Fixed the angles.py script used in the system tests.

The heteronuc arg to structure.vectors() has been removed.

Modified the structural API stub method atom_loop() to accept the model_num_flag arg.

Modified the Scientific Python API atom_loop() method to return the model number when asked.

Added the unit arg to the vectors() fn. This might be useful in the future.

Removed the heteronuc arg from vectors(), and placed the proton name into spin.attached_proton.

Redesigned the structure.vectors() user function again, again removing the heteronuc arg.