Use global cookie domain

When using cookie storage, the global cookie domain is not respected. There is a note in code about deliberately doing this to avoid setting the domain of the cookie to an invalid domain such as '.localhost'. However, in that case, the global $cookie_domain variable is misunderstood -- the whole point of it is so that it can be overwritten in settings.php for a variety of multisite installations. (See the comments in default.settings.php)

So the attached patch reinstates the use of the global $cookie_domain variable. If people are getting their cookies set at '.localhost', then the variable needs to be set correctly in Drupal's settings.php file, but this module should not need to reimplement this.