relax SVN archive

The top level PipeContainer objects are now written to the XML results file.

Changed the references from xml to xml_data_pipe.

Renamed the xml module to avoid a name clash with the python xml module.

Added some imports and create the empty XML document object.

Updated the RelaxFileOverwriteError message to display a bool value rather than int.

The generic_fns.xml module is now accessed directly from the generic_fns code.

Added a module for the creation and parsing of XML documents representing a data pipe.

The write() function now catches and translates the special dir name 'pipe_name'.

Changed the default values of the args of the results.write() user function.

The dir arg now defaults to the special value of 'pipe_name' and the format arg defaults to 'xml'.

Changed the args to the results.read() user function.

The dir keyword now defaults to None and the format arg no longer exists, as it is assumed that
relax will autodetect the file format.