Support redirects on "unsafe" HTTP methods

[jsvd]

The httpclient library used by this mixin is very conservative when it comes to status code handling, that only does what MUST be done (not what MAY be done) according to the RFC7231.

According to this RFC, requests MAY be automatically redirected but caution should be taken for unsafe methods (safe: GET/HEAD/OPTIONS, unsafe: POST/PUT/DELETE/PATCH).

The existing setRedirectsEnabled flag will only redirect on safe methods, but it may be desirable to redirect on PUT/POST if the users so wishes, by having this behavior behind an "off-by-default" flag.