Choose one test to confirm that explicit unicode filters are okay.

Make teardown safer too.
Older cookie libraries need the cookie to be an old-style string.

So, we do the dance. It's getting rather convoluted...
Accept header handing must be resilient in the face encodings

Depending on context header values may be bytes/str or string/unicode.

This was exposed by different versions of wsgi-intercept, one of which
is better about header encoding handling.
Provide an explanatory comment for exception in filter parsing.
Adapt query handling to be flexible in the face of library differences.

query parsing changes across python versions