Change the password of a certain user in a specific realm.
This method in fact adds the user whith the new password after deleting the user.
the user whose password should be changed
the realm the user is in
the new plaintext password
Returns TRUE on success, PEAR_Error on failure.
Table 43-1. Possible PEAR_Error values
|FILE_PASSWD_E_USER_NOT_IN_REALM||user doesn't exist in the supplied realm|
|FILE_PASSWD_E_INVALID_CHARS||user or realm contains illegal characters|