relax SVN archive

Clarifications and minor expansion of the release checklist document.

Bug fix for the pcs.structural_error user function.

The user function now uses a real multivariate normal distribution for sampling atomic positions.
The previous random unit vector + univariate Gaussian sampling does not correctly reproduce the
multivariate normal distribution.

Updated the relax version number to 4.0.3 on the http://www.nmr-relax.com/api/index.html webpage.

Updated the relax API documentation at http://www.nmr-relax.com/api/4.0/ to version 4.0.3.

Updated the relax HTML manual at http://www.nmr-relax.com/manual/index.html to version 4.0.3.

Updated the http://www.nmr-relax.com/download.html webpage for the relax 4.0.3 release.

Backported the relax 4.0.3 CHANGES file changes to trunk.

The command used was:
svn merge -r28265:28266 svn+ssh://bugman@.../svn/relax/tags/4.0.3 .

Updated the CHANGES file for relax 4.0.3.

Added the relax 4.0.3 manual to the repository.

Updated the version number to relax 4.0.3.