relax SVN archive

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.

Shifted the hybridisation info from the global element to its own element.

Shifted all the variables of PipeContainer into the 'global' element.

The 'type' variable is now initialised within the __init__ method.

Added the 'hybrid_pipes' object to the XML document as this will eventually only be a list of str.