This pull request addresses #2185, and supports cross-scheme redirects in the *lfsapi.Client type.

The issue is that, even though Go's *net/http.Client supports redirects (in response to a 3xx status code) directly, we explicitly disable that as^[1]:

httpClient := &http.Client{
  Transport: tr,
  CheckRedirect: func(*http.Request, []*http.Request) error {
    return http.ErrUseLastResponse
  },
}

So we're forced to handle HTTP requests ourselves in the lfsapi.Client.doWithRedirects function. This is fine, since we already have logic to rewind the body and copy the headers over.

As an aside, ideally we could hook into the net/http.Client.CheckRedirect field to hand this responsibility over to the net/http package, but the HTTP client follows an older RFC (which it maintains for backwards compatibility reasons) that prevents the client from copying the HTTP verb the request was sent with when a 301, 302, or 303 response code is given: (see: https://github.com/golang/go/blob/go1.8.1/src/net/http/client.go#L423-L429). We cannot work around this, so we must handle it ourselves.

This pull request expands the list of 3xx response codes that we will redirect from and increases the permissiveness of HTTP header copying to only check that the from->to host transition is the same, without checking the scheme.

Closes: #2185

/cc @git-lfs/core @larsxschneider