Post slug improvements

[markjaquith]

1. Right now, a post ID is shown as the post slug unless a slug is manually entered. Instead, it should show the dynamic slug generated from the title. Ideally, as the title is updated. (maybe using onblur to see if the typed-in title has changed, and doing a quick AJAX request to see what the dynamic slug would be).
2. There is no way to tell the difference between a tentative slug, and a locked-in slug (either by choice, or by hitting "publish"). Perhaps the highlighting could go away and the slug could be bolded to indicate that it is set.