relax SVN archive

Fix for the grid search with the isotropic cone frame order models having the 'cone_theta' parameter.

Added a check in the frame order grid search so that the inc list size matches the number of parameters.

Parameters can be fixed to the original values during the frame order grid search.

The grid_search() user function argument incs can now be a list with None elements to fix parameters.

This will only be used in the frame order optimisation for now.

arg_check.is_int_or_int_list() can now allow for None list elements.

The model can be overwritten by frame_order.select_model().

Missing relax error import.

frame_order.ref_domain() now only updates the model info if the model is set.

Removed the model check from frame_order.ref_domain().

Fix for the test_compile_2nd_matrix_rotor_point1() unit test.

The compile_2nd_matrix_rotor() function was being incorrectly called.