relax SVN archive

Expanded the relaxation curve-fitting chapter of the manual to include descriptions of the models.

A new section at the start of this chapter has been added to explain the different models and their
equations. This was taken from the script mode section and expanded to include the new saturation
recovery experiment.

Improvement for the relax_fit.select_model user function in the GUI.

Unicode text is now being used to display the parameters as R_x and I_0 and to show an infinity
symbol in the Iinf parameter. The Rx and Iinf parameters have been added to lib.text.gui to allow
this.

More editing of the relax_fit.select_model user function.

The IR and SR abbreviations have been added, and a lot of text cleaned up.

Implemented the target functions for the inversion recovery exponential curve.

In the Python target function class Relax_fit_opt, the new func_inv(), dfunc_inv() and d2func_inv()
methods have been created as wrappers for the new C functions. These are aliased to func(), dfunc()
and d2func() in the __init__() method.

The target_functions/exponential_inv.c C file has been created with the functions exponential_inv(),
exponential_inv_d0(), exponential_inv_dIinf(), exponential_inv_dR(), exponential_inv_dI02(),
exponential_inv_dIinf2(), exponential_inv_dI0_dIinf(), exponential_inv_dR_dI0(),
exponential_inv_dR_dIinf() and exponential_inv_dR2() have been created to implement the function,
gradient, and Hessian for the equation I(t) = Iinf - I0*exp(-R.t).

In the target_functions/relax_fit.c file, the functions func_inv(), dfunc_inv(), d2func_inv(),
jacobian_inv() and jacobian_chi2_inv() have been created as duplications of the *_exp() functions,
but pointing to the exponential_inv*() functions and adding the Iinf dimension.

Another change for the relaxation curve-fitting covariance_matrix() API method to handle all models.

The scaling matrix diagonalised list of 1.0 values now has the same number of elements as there are
parameters.

Big bug fix for the error_analysis.covariance_matrix user function.

The model_info structure is now being passed into the get_param_names() API method, as required by
the API.

Updated the relaxation curve-fitting get_param_names() API method to handle all models.

This now simply returns the spin container 'params' list, allowing all models to be properly
supported.

The errors in the Relax_fit.test_saturation_recovery system test are now reasonable.

They have been set to 5% of Iinf so that the chi-squared value during optimisation is more
realistic.

Updated the relaxation curve-fitting covariance_matrix() API method to handle all models.

The check for the 'exp' model type has been eliminated, and the parameter vector is assembled using
the flexible assemble_param_vector() function rather than manually constructing the vector.

Expanded the relax_fit_saturation_recovery.py system test script.

This now calls the error_analysis.covariance_matrix user function to test that code path.