Check Expire settings for hostname inclusion

I don't believe purge should check for the specific option "Include base URL" from Expire Cache (we would rather do without that dependency right?). Rather, it should check if the passed purge_url includes the host and generate the purge_url based on that, taking from global $base_url and $base_path if only a path was passed rather than a full url. Please consider my patch.

btw.: I couldn't download 7.x-1.x-dev or 7.x-2.x-dev therefore I patched 7.x-1.5-rc1 . Please excuse if you already have this sorted.