relax SVN archive

Added the pickle arg to state.save().

This allows the relax state - the contents of the relax data store - to either be saved as XML or as
a pickled object.

Created the relax data store is_empty() method.

Updates to the load_xml() function. This now does something!

Removed trailing whitespace.

Shifted the results.write() force arg to the end.

Bool args should be last!

The relax data store to_xml() method now can add all data pipes to the XML file (or a subset).

The results.write() method now asks to_xml() for just the current pipe to be stored, whereas
state.save() supplies no 'pipes' argument to have all pipes stored.

The save_state() function now calls the relax data store to_xml() method.

This method is currently only for one data pipe, and is used by the results writing user function.

Added the pickle flag to save_state().

This defaults to True to prevent relax failures during the XML file implementation.

Redesign of the relax state loading for adding support for a XML formatted state file.

Half of the load_state() is now in load_pickle(), and a new function load_xml() added.
The determine_format() function will tell if the file is a pickle or XML file, and then
load_pickle() will run the appropriate loading function.

A few fixes for the test_write_read_pipes() system test.