Refactor response cookie handling to use our new Request#cookie_jar.
Instead of creating a jar from scratch, make a copy of the request's
cookie jar and populate it with any additional cookies from the response
headers.
Also refactor the redirection code to use this cookie jar, which solves
the question of how to handle cookies from the original request.
It is redundant and confusing to pass both the Request args and the
Request when creating a RestClient::Response. Instead, when the response
object needs to read args from the request, access them on the request
object itself. For determining the HTTP method of the request, switch to
calling RestClient::Request#method.
Also normalize the Request#method to be a lowercase string. This makes
handling of redirection and other method-specific functionality actually
work regardless of how the method was provided to Request.new (:get,
'GET', 'get').
Fixes: #461Fixes: #462Fixes: #463
