Tighten up the handling of $wgEmailConfirmToEdit , plus related functionality:

Tighten up the handling of $wgEmailConfirmToEdit , plus related functionality:

* Bug 11620 - Added call to User::isValidEmailAddr during accout creation.
* Bug 11629 - If $wgEmailConfirmToEdit is true, require people to supply an
  email address when registering.
* adding "prefs-help-email-required" message (which says an email address is required)
  to complement the existing "prefs-help-email" (which says an email address is optional).
  The former makes sense when $wgEmailConfirmToEdit is true, whereas the latter makes
  sense for the default behaviour (which is for $wgEmailConfirmToEdit to be false).
* Using the "prefs-help-email-required" message in Special:Userlogin and Special:Preferences
  when it makes sense to do so.
* Removing EditPage::userNotConfirmedPage() - as far as I can tell, it is not being
  used internally, or by any extensions. Furthermore, its functionality is superceded by
  the $wgEmailConfirmToEdit global and the check on it in Title.php