relax SVN archive

A PDB file now can be specified without the '.pdb' ending.

Initialized merge tracking via "svnmerge" with revisions "1-6651" from
svn+ssh://bugman@.../svn/relax/1.3

Created a development branch for implementing some basic RDC and PCS dynamics analyses.

Fix for the loading of the diffusion tensor if it doesn't exist - don't do it!

Added a system test for the reading of an empty results file.

This should test out all reading compatibility issues in all analysis types.

Bug fix for the SpinList.to_xml() method.

The return_data_desc() function is only called if it exists.

Added an empty 1.3 results file to the test suite.

Updated and fixed the relaxation curve fitting data_names() method.

Activated the results system tests.

Wrote a system test for writing an empty results file.