format-patch: fix rfc2047 address encoding with respect to rfc822 specials

format-patch: fix rfc2047 address encoding with respect to rfc822 specials

According to RFC 2047 and RFC 822, rfc2047 encoded words and and rfc822
quoted strings do not mix. Since add_rfc2047() no longer leaves RFC 822
specials behind, the quoting is also no longer necessary to create a
standard-conforming mail.

Remove the quoting, when RFC 2047 encoding takes place. This actually
requires to refactor add_rfc2047() a bit, so that the different cases
can be distinguished.

With this patch, my own name gets correctly decoded as Jan H. Schönherr
(without quotes) and not as "Jan H. Schönherr" (with quotes).

Signed-off-by: Jan H. Schönherr <schnhrr@cs.tu-berlin.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>