Apply real username to editor page on mailouts

Note that we could be hooking getCanonicalUrl
or also EmailUser, but both would lead to an
excess of process where all the information is
already available @ UserMailer.php, hence we
are introducing a 3-line hack there.

If, in the future, we get some hook for mail template
variables, that would be the place to hook. Until then
we'll survive with the hack.