ActUser objects can be germinated from various sources:

1) a get_user call
2) a get_user_by_id call
3) a list_users call

Because of this, there may be one ActUser objects in
the wild holding the users session lists, and another
holding all the user information returned from the account
service.

This commit makes sure at the, end of the day, we consolidate
all the information we know, so some doesn't get dropped on
the floor.

Related to gnome bug https://bugzilla.gnome.org/show_bug.cgi?id=671858