Global icon link should stay on edit host

Description

Steps to reproduce

1. In admin, under Manage Web Sites, add a public URL and an edit URL.
2. Go to Admin or Dashboard page via edit URL.
3. Click the global icon in the top right corner.

Expected: Goes to the edit site.
Actual: Goes to the live site.

As reported:
"The primary reason to have a separate edit host is to not have logged in editors on the public facing server(s), so by navigating away from the edit host, you can't easily go back to the edit host. They will be different domains too, so the cookie (for regular forms auth) will probably not present on the front-ends, even if it allowed editors to log in"