Better mimc the user_profile page's submit handler

Other modules, such as Force Password Change → , add additional fields to both the `$account` and the form to trigger their own changes. The `change_pwd_page_form_submit()` function creates an `$edit` array with only the `pass` field, and effectively strips out these other fields.

The submit handler should better mimic the `user_profile_form_submit()` handler, or call it directly, to preserve core's user profile editing semantics.