relax SVN archive

Updated many system test scripts for the new relax_data.read() user function interface.

Fixes for the back end of the relax_data.back_calc() user function.

The missing ri_id arg situation was not being handled and spin container ri_data_bc structure was
being constantly overwritten.

Simplifications for all of the diffusion tensor system tests.

The relax_data return_value() function can now handle missing data.

Fixes for the setting up of model-free optimisation.

Fix for the back_calc_ri() method.

Updated the model-free back_calc_ri() method for the new relax data ID string design.

Update of the palmer.py Modelfree4 system test script for the new relax data ID string design.

Converted all spin.frq[0] to cdp.frq[cdp.ri_ids[0]] as the spin object 'frq' no longer exists.

Epydoc docstring fixes.