alt login permissions now assignable by role. use USERNAME_MAX_LENGTH constant. alt logins now work for password reset requests.

properly unset alt_login field to avoid entry into data column of user table. better validation -- alt_login and username cannot be changed to be identical, and user cannot change username to an existing alt_login name.

#104168 -- Alt login field appearing in the user registration page. put setting into admin/user/user page to allow disabling the alt login form element on user registration.

#104167 -- alt login deleted when updating user profile. patch by hunmonk. only fire the update code if the update is coming from the save category.