doctests aren't run

[jaraco]

While working on another issue, I was adding some code. When I added the code, I added a couple of doctests to document and test the basic behavior, but when I ran the tests with -k httputil (since the doctests were in httputil), the tests weren't run. It would be preferable for doctests to be exercised when they exist.

[jaraco]

As a temporary workaround, I was able to run .tox/python/bin/python -m doctest cherrypy/lib/httputil.py to exercise and validate the new tests.