git-format-patch does currently not parse user supplied extra header
values (e. g., --cc, --add-header) and just replays them. That forces
users to add them RFC 2822/2047 conform in encoded form, e.g.

    --cc '=?UTF-8?q?Jan=20H=2E=20Sch=C3=B6nherr?= <...>'

which is inconvenient. We would want to update git-format-patch to
accept human-readable input

    --cc 'Jan H. Schönherr <...>'

and handle the encoding, wrapping and quoting internally in the future,
similar to what is already done in git-send-email. The necessary code
should mostly exist in the code paths that handle the From: and Subject:
headers.

Whether we want to do this only for the git-format-patch options
--to and --cc (and the corresponding config options) or also for
user supplied headers via --add-header, is open for discussion.

For now, add test_expect_failure tests for To: and Cc: headers as a
reminder and fix tests that would otherwise fail should this get
implemented.
Signed-off-by: NJan H. Schönherr <schnhrr@cs.tu-berlin.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>