relax SVN archive

Expanded the minimise.grid_zoom user function documentation.

A few sentences about the limitations of the algorithm have been added.

Large expansion of the minimise.grid_search user function documentation.

The previous documentation was essentially non-existent.

Alphabetical ordering of the minimisation user functions in the user_functions.minimisation module.

Changed the minimise.grid_zoom user function.

The zoom level can now be any floating point number or integer, including negative values. The user
function docstring has been significantly expanded to explain the entire zooming grid search
concept.

Removed a debugging printout.

Modified the zooming grid search algorithm.

If the zoom level is negative, hence the grid will be larger than the original, the checks that the
grid is within the original are no longer active.

Implemented the zooming grid search.

If the zoom level is set to any value other than 0, then the grid width will be divided by
2**zoom_level and centred at the current parameter values. If the new grid is outside of the bounds
of the original grid, the entire grid will be translated so that it lies entirely within the
original.

The rx parameter of the relaxation curve-fitting analysis now has 'rad.s^-1' units defined.

Modified the behaviour of the parameter object units() method.

If the unit is set to the default of None, this method will now return an empty string instead of
None.

Fix for the _prompt.test_diffusion_tensor.Test_diffusion_tensor.test_init_argfail_params unit test.

As the diffusion tensor can now be initialised as None, the None value can be accepted and a
different RelaxError is raised when the params argument is incorrectly supplied.