RAC : Don't filter model global variables in the task
Currently when executing the RAC, global variables are filtered from the task when they are not free in the term that is checked. It was probably done because the generated models can assign inconsistent values to global variables, leading to bad counterexamples. However, this filter can in several cases make the counterexamples impossible to verify, therefore it should be removed. To avert the generation of inconsistent values for global variables, the solution is to avoid having abstract declarations of such variables, as done in MR !899 (merged).