relax SVN archive

Overhaul of the chi-squared gradient and Hessian functions.

The original functions have been renamed to dchi2_element and d2chi2_element as these calculate the
gradient for element j and the Hessian for element {j, k}. Two new functions, dchi2 and d2chi2 have
been written to calculate the full gradient and Hessian in one function call.

These changes will temporarily break a lot of code!

Improvements to the chi-squared value, gradient, and Hessian docstrings.

Fixes for the alignment tensor gradient function code.

Wrote functions for all the alignment tensor gradients.

Import fixes.

Split the rdc module in half, shifting the alignment tensor components into their own module.

Started to add the framework for the addition of gradients and Hessians.

Made the spin_name arg optional in the spin.create() user function.

Started the modification from 'devnull' to tempfiles.

This is as proposed by Edward d'Auvergne to catch the creation of a well formatted and non empty
tensor pdb file and was discussed in a post at:
https://mail.gna.org/public/relax-devel/2008-07/msg00029.html (message ID:
7f080ed10807081248r1f0fda8axd17768bb841efe71@...)

Inverted the population scaling factor in __assemble_scaling_matrix().