relax SVN archive

Fixed the initialisation of the variables pcs, pcs_vect, and pcs_dj.

Fixed the call to __minimise_setup_pcs().

Fixes for the __minimise_setup_pcs() method.

Multi-dimensional arrays were not being properly created or referenced.

The load_spins() function is now either loading the average or all atom positions.

Renamed the ave arg of structure.load_spins() to ave_pos.

Added the ave arg to the structure.load_spins() user function.

Redesigned the __minimise_setup_pcs() method.

Fixes for the PCS constant, as it is dependent on the indices i, j and c.

These are:
i, the experiment or alignment index,
j, the spin index,
c, the state index.

Added Boltzmann's constant to the physical_constants module.

Wrote the pcs_constant() function to calculate the pseudocontact shift constant.