#17956 is reply fails if message in local mail folder
fix (by ducarroz) is to remove the temporary code.
#18084 is sending email fails in certain cases
the problem is we were sending the wrong info to the SMTP server.
when we sent "MAIL FROM: <address>" to the SMTP server we sent
the smtp username and not the full name built from the identity.
most of the changes are to support passing the identity around.
I also added code so that the smtp username is used on the mailto url spec.
we'll need that later, when we support multiple smtp servers and ESMTP.
r=alecf
a=chofmann
