relax SVN archive

Added a missing import and fixed an incorrect reference to the data pipe container.

Shifted the calculation of the paramagnetic centre from __minimise_setup_pcs() to centre().

The data pipe arg is now accepted by the centre() function.

Added the pipe arg to the pcs.centre() user function.

Wrote the num_data_points() method for determining n.

Wrote the model_statistics() method.

Bug fixes and expansion of the __linear_constraints() method.

The bug fix is that the b array was not being scaled! This is essential when diagonal scaling is
active.

The added feature is that the pN weight of state N, which is not a parameter of the model, is now
constrained to be between 0 and 1. This is because the value is equal to 1 minus the sum of all
other probabilities, hence linear constraints can be created.

Added the ability to reload alignment tensors from the XML results file into the relax data store.

Ported r7099, r7100, r7101, r7103 and r7104 to the consistency tests code.

Fix for the test_display_argfail_tensor() unit test.