relax SVN archive

Partial fix for bug #12407 (https://gna.org/bugs/index.php?12407).

This catches the "TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'" error. If
the local or global tm is missing for some reason, the eliminate function returns False indicating
that the model has not been eliminated.

Fix for the test_tm_51ns() system test.

The model 'tm4' is set rather than 'm4'.

Conversion to bools in determine_model_type() and a fix for bug #12408 (https://gna.org/bugs/?12408).

All internal flags in the method have been converted to Booleans. This commit also contains a bit
of a fix for bug #12408. The bug was a false alarm and now determine_model_type() raises a more
relevant RelaxError.

Created a system test for model-free model elimination when local tm > 50 ns.

Completed the fix for bug #12407 (https://gna.org/bugs/index.php?12407).

This latest problem was caused by the use of the wrong Boolean operator in the model-free
eliminate() method. The method has also been converted to return the Booleans True or False.

Partial fix for bug #12407 (https://gna.org/bugs/index.php?12407).

The model-free assemble_param_names() method was not returning the parameter names. This could
affect much more than model elimination!

Missing import fix for the model elimination system test.

Fix for bug #12406 (https://gna.org/bugs/?12406).

The issue was that the force flag should have had a default value of True so that value.set() can
overwrite existing parameters.

Fix for the system test of the model elimination module.

The setUp() method has been added and it creates a data pipe to store the data.

Created a system test for model elimination of a model-free model.