FollowRedirects should handle different intermediary response types

[christhekeele]

Currently, FollowRedirects will try to parse the body of 3xx responses with the requested Accepts type, rather than the intermediary Content-Type of the redirect response. This can cause it to blow up when, for example, a JSON API request issues a redirect with an HTML body as noted in rails/rails#17194.

We could either prevent it from actually doing the parsing on redirects (bad idea? possible with the way the middleware stack works?) or make it honor the intermediary Content-Type when parsing the body.