* Do not interpret non-ASCII bytes in "Location" and percent-encode them
Fixes GH-2321
The idea is to not guess the encoding of "Location" header value
and simply percent-encode non-ASCII bytes,
which should then be re-interpreted correctly by the remote website
in whatever encoding was used originally.
See https://tools.ietf.org/html/rfc3987#section-3.2
This is similar to the changes to safe_url_string in
https://github.com/scrapy/w3lib/pull/45
* Remove unused import
