relax SVN archive

Replaced the way to calculate the chi2 Jacobian, for exponential fit in minfx.

This is only for the test class, but reuses library code.

This should make it much easier in the future to implement chi2 gradient functions to minfx, since it
is only necessary to implement the direct gradient of the function, and then pass the direct gradient to chi2 library, which turn it into
the chi2 gradient function which minfx use.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.

Tried implementing getting the chi2 gradient, using target_function.chi2.dchi2().

The output seem equal.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.

Better error checking for the specific_analyses.relax_disp.average_intensity() function.

This function would fail with a traceback if a peak intensity error analysis had not yet been
performed. Now it fails instead with a clean RelaxError so that the user knows what is wrong.

Better error checking in the relaxation dispersion overfit_deselect() API method.

The model must be set for this procedure to work, and the method now checks that this is the case.

Removed all references to test values which was received by wrong weighting.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.

Swithced in estimate_r2eff_err() to use the chi2 Jacobian from C code, and Jacobian from python code.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.

Fix to systemtest test_estimate_r2eff_err_methods, after modification of weighting.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.

Fix to weight properly according to if minimising with direct Jacobian or chi2 Jacobian.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.

Increased the number of time points for exponential curve fitting to 3.

Fix to systemtest: test_estimate_r2eff_err_auto, which now checks the values for the direct Jacobian.

task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.