Improve compliance to the WSGI spec.

When trying to use the paste.lint middleware in development, I ran into a few issues
with zope.server's adherence to WSGI.

This PR makes the following changes:

- Call close method if present on iterables returned by start_response.
- Don't include non-string values in the CGI environment (CHANNEL_CREATION_TIME).
- Always include QUERY_STRING to avoid the cgi module falling back to
  sys.argv.
- Add tests based on paste.lint middleware.