"display_all" is too coarse, and we should be letting event handlers
make the appropriate decision on what to display and when. This
duplicates some code, but it's now very clear in the event handlers
what's getting shown.
Throw a 404 if we try to view the user profile for a missing user.
The only feature change in this should be that we now display the
name, full name and website for a user to any other registered user,
which makes sense since these are typically public fields.
Don't show any of the edit buttons unless identity::is_writable()
Fixes ticket #585.
Separate out the password change form from the regular edit user form.
Require the old password to enter a new one. While I'm at it, roll
the password strength javascript into a Form_Script element so that we
can get rid of the old view (which incidentally fixes a bug where the
password strength meter would go away on form errors).
