[web] return 403 for Unauthorized, not 401 401 is reserved to HTTP authentication. Just because it's also called "unauthorized" doesn't mean it's the same as cubicweb's Unauthorized exception. Closes #3648809.

from os.path import join
assert __file__.endswith(join('scripts', 'script1.py')), __file__
assert '__main__' == __name__, __name__
assert [] == __args__, __args__