integration with profile module, and real notify change emails

The following patch makes a few useful changes:
- finds out added profile fields, and proposes their values for the email
- send the `update profile' email only *after* the user saves (old version is bogus, the update hook is called ways too early).
- avoid emailing for nothing during profile updates: the new version creates before/after emails, and sends email only when things changes. This is needed for our organization, otherwise we get emails when people change their password (which we can't access anyways).