Possible replacement for code 301 Moved permanently

[colin-adams]

Experimental RFC 7238 defines a new response code 308 Permanent redirect, intended to avoid the ambiguous response to 301 Moved permanently. The latter is used by WSF_METHOD_HELPER and WSF_PUT_HELPER. In the latter case particularly, the response allows the client to retry the PUT as a GET, whereas 308 does not allow this.

In the future, we might want to support 308 (if it becomes widely used). For now, no action.