Fix Intersection Complement simplification
sets: added tests to imporove the coverage

* The overall coverage of sets module is increase to 96% from 93%
    * sets.py:: now: 96% earlier: 93%
    * fancysets.py:: now: 97% earlier: 90%
Merge pull request #7865 from hargup/complement_fixes

Fix Intersection Complement simplification
Remove .is_finite assumption

fixes #5393
fixes #5385
fixes #7007