funcky redirect on logout only when needed.
experimental feature to grant role at runtime.

by aangel, Dave Cohen: improved tab support by storing configuration data, default tab callback and hook_fb_tab.

by aangel, Dave Cohen: add parameter to event callback.  Otherwise, post-remove events have no way to know which application is removed.

misc comments

deleted some obsolete code

changed _fb_js_fbu param to avoid confict with "fb_..." params from old facebook api.  Still not working on canvas pages though.

Also improved comments to fb_scrub_urls().