Improve adherence to the WSGI spec.

- Call close method if present on iterables returned by start_response.
- Don't include non-string values in the CGI environment.
- Always include QUERY_STRING to avoid the cgi module falling back to
  sys.argv.
- Add tests based on paste.lint middleware.
Merge pull request #1 from zopefoundation/kilink-wsgi-compliance

Improve compliance to the WSGI spec.