relax SVN archive

Fixes for the target_functions.relax_fit C module unit tests.

All values are now set to floats to avoid integer division issues.

Created a unit test to check the dfunc() function of the relax_fit C module off the minimum.

Added a script and log file for calculating the numerical gradient for an exponential curve.

This uses the data at http://thread.gmane.org/gmane.science.nmr.relax.devel/6807/focus=6840 and
calculates the gradient using the scipy.misc.derivative() function both at the minimum and at a
point away from the minimum. The values will be used to construct a unit test to check the C module
implementation.

Added several comments to the R2 eff estimate module.

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

The relax_fit C module unit tests now check if the parameter scaling is functional.

Created 2 unit tests for the target_functions.relax_fit relax C module.

These check the func() and dfunc() Python methods exposed by the module.

Big cleanup of estimate R2eff module.

This is to make the documentation more easy to read and understand.

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

The I0 and R parameter indices are now defined in the target_function/relax_fit.h header file.

This is to abstract the exponential curve parameter indices even more.

The parameter index is now passed into exponential_dI0() and exponential_dR().

This is for the relaxation curve-fitting C module so that the indices are not hardcoded.

Modified all of the exponential curve functions and gradients in the C target function module.

Instead of passing in the parameter vector, now the I0 and R values are passed in separately. This
is for greater code flexibility as the parameter order does not need to be known.