relax SVN archive

Improvements to the optimisation tests and fixes for bug #14173, bug #14174, bug #14175, bug #14176, bug #14177, bug #14182.

The bugs were reported by Jack Howarth (https://gna.org/users/jhowarth) and Seb
(https://gna.org/users/semor).

The architecture info and optimisation stats for a number of systems have been added to the file for reference.

Added a function intro text for the script() user function.

Fix for the script() user function.

The function intro flag at the end of executing an external script was not being restored.

The frame order minimisation now first checks if the tensor reductions have been specified.

Created the new maths_fns.rotation_matrix.R_to_euler_zyz() function and associated unit test.

Large code refactorisation - the current data pipe is now in __builtin__.cdp.

The result is the removal of 484 calls to generic_fns.pipes.get_pipe() to get the current data pipe.

Added a system test for the frame order 'rigid' model with no tensor rotations and no motion.

Added a missing alias for the current data pipe.

Rearrangement of the handling of frame order models.

The tensor rotation Euler angles are now model independent, the 'rigid' model is better supported,
and a clear isolation of the isotropic cone model has been made.

Added __description__ strings to the user function class relax help strings.

The __strip_lead() method has been added to User_fn_class to remove leading whitespace from the
__description__ strings.