Background Jobs: Consider "Local" REQUEST mode

Ran across an issue in [ZD thread 468419](http://woothemes.zendesk.com/agent/tickets/468419) for which a development server was used with a hosts file to point to the domain.

Tracked this down with @ragulka to the way requests are sent. The background processing uses cURL to fire non-blocking HTTP requests to the site, but the requests are using `wp_safe_remote_post()` -- as such, they need a full URL to make the request, so an IP for a development server can't be used without a hosts file on the server as well.

Rather than requiring a hosts file on the dev server as well, we can investigate whether an IP address can be used and see if we can disable WP auto-redirecting on those requests. Perhaps a "development mode" setting or set of filters to enable dev mode and the use of an IP address for requests. Not sure if possible yet, but worth a look into.