the response-content-type, response-content-language, response-expires,
response-cache-control, response-content-disposition, and
response-content-encoding request parameters can be supplied to control
the response headers of an S3 GET request. allow providing these to
S3Object.url_for and have them included in the URL. bring along the
other recognized parameters as well, while we're at it.
also, make sure these parameters make it into the canonicalized request