Headers.add fails with unicode

[tko]

# encoding: utf-8
from werkzeug.datastructures import Headers

headers = Headers()
headers.add('Content-Disposition', 'attachment', filename=u'åäö.html')

Traceback (most recent call last):
  File "test.py", line 5, in <module>
    headers.add('Content-Disposition', 'attachment', filename=u'åäö.html')
  File "/tmp/werkzeug/werkzeug/datastructures.py", line 1105, in add
    _value = _options_header_vkw(_value, kw)
  File "/tmp/werkzeug/werkzeug/datastructures.py", line 841, in _options_header_vkw
    for k, v in kw.items()))
  File "/tmp/werkzeug/werkzeug/http.py", line 214, in dump_options_header
    segments.append('%s=%s' % (key, quote_header_value(value)))
  File "/tmp/werkzeug/werkzeug/http.py", line 167, in quote_header_value
    value = str(value)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-2: ordinal not in range(128)

[untitaker]

See pallets/flask#1286

[javabrett]

I am visiting this issue while making some commentary in the same area, but it seems that it should be closed/won't-fix, since non-ASCII and non-latin1 representations in HTTP headers can only be done in accordance with RFC 8187.

Please close.