relax SVN archive

Fixes for the PipeContainer methods.

Shifted the generic_fns.xml_data_pipe.write() fn to the PipeContainer.xml_write() method.

Updates to many docstrings.

Added a 'desc' attribute to the pipe XML element.

Made the diff_tensor XML element optional, as the object may not always exist.

Fix for the test_read_results_1_2() system test.

Changed the variables initialised by the PipeContainer.__init__() method.

Many are no longer initialised and the hybrid_pipes dictionary has been converted to a list.

Added the structural information to the XML results file.

Docstring improvements.

The hybrid element is no longer returned.