relax SVN archive

The GUI test _execute_uf() base method now handles non-keyword args, by converting them to keyword args.

All system test scripts are now executed through the base script_exec() method.

This allows them to be run in the GUI tests as well.

Fix for the file selection and directory handling in the GUI base test _execute_uf() method.

This now handles the situation of when no directory argument is supplied.

The execute_uf() method is now private!

Final fix for the rdc_tensor.py N-state model system test script.

Added all of the N-state model system tests as GUI tests.

Modified the GUI tests so that they can operate in the same way as the system tests.

Now entire test suite classes can be executed in isolation by typing, for example:

$ relax --gui-test N_state_model

Fix for the rdc_tensor.py N-state model system test script minimisation call.

Converted all of the N-state model scripts to use the new self._execute_uf() interface.

Added some error checking for the system test class execution.

This is for better user feedback for when the user supplied class does not exist.