(bug 34421) duplicate Subject / wrong To: headers in mail

(bug 34421) duplicate Subject / wrong To: headers in mail

This fixup our mail sending system which duplicated the Subject and To: header.
In some conditions it used only the email address for the From: field skipping
the username ($dest in old code only contains the email address).

Mails sent to a single recipients will look alike with mail() or PEAR Mail.
For multiple recipients:
 - php mail() will show the recipient email and 'undisclosed-recipients:'
 - PEAR Mail will only show 'undisclosed-recipients:'

Reverts r111820
Follow  r111819
Fixup    r93397