Fixed a bug where mail messages were malformed when using the Sendmail
transport on Unix systems with certain versions of sendmail (e.g.
Postfix < 2.9). Specifically, message headers spilled into the body
and the body text was double-spaced.

The source of the problem was the use of CRLF as the EOL sequence
when sending messages via PHP's built-in mail() function on Unix
systems. Despite what the PHP manual says, LF should be used as the
sole EOL character on Unix. This is because mail() is a wrapper for
sendmail on Unix and does not speak SMTP except on Windows.
Cast a wider net for EOL translation. The to and subject headers were
being independantly wrapped. Now we convert line-endings on $to, $subject,
$body and $headers immediately before calling mail().
Merge branch 'mail-fix-eol' of git://github.com/stewartlord/zf2 into hotfix/3757
Merge branch 'hotfix/3757'

Close #3757