Changing "private" to "protected" on a few functions in User.php

This is required for auth plugins to be able to send customized
email confirmation and migration emails.  For example, we need to
send emails from CentralAuth that will both confirm the email
address and then run through Special:MergeAccount attempting to
attach as many local accounts as possible.

Change-Id: If281aa6219e5a0b80252b0deac7ee0c4f74c3d58