restructured hook_user to allow easier reuse of buddylists elsewhere

added rudimentary online status indicator for buddies. removed dependency on profile module altogether. changed theming of buddylisting pages, so if you have a heavily themed buddylist page, beware of changes.

backporting all changes from cvs version done by quicksketch; adding buddylistinvite module to 4-7 branch

#55230, plus made the dependency on profile module visible under admin/settings/buddylist instead of on the users' buddylist pages

major update. added buddy groups. will also contribute an node access control module which uses these groups ... fixed many many bugs/ugliness, and probably introduced a few. if you are happily using buddylist now, you might wait a while until these changes get exercised by some sites ... database update required. i added a column and changed the indices. see the buddylist.mysql file

* use calls to theme_user_list()

* theme('placeholder') usage

- Renamed check_query() to db_escape_string().  Commit announced on the mailing list.