format-patch: generate MIME header as needed even when there is format.header
Earlier, the callchain from pretty_print_commit() down to pp_title_line()
had an unwarranted assumption that the presense of "after_subject"
parameter, means the caller has already output MIME headers for
attachments. The parameter's primary purpose is to give extra header
lines the caller wants to place after pp_title_line() generates the
"Subject: " line.
This assumption does not hold when the user used the format.header
configuration variable to pass extra headers, and caused a message with
non-ASCII character to lack proper MIME headers (e.g. 8-bit CTE header).
The earlier logic also failed to suppress duplicated MIME headers when
"format-patch -s --attach" is asked for and the signer's name demanded
8-bit clean transport.
This patch fixes the logic by introducing a separate need_8bit_cte
parameter passed down the callchain. This can have one of these values:
-1 : we've already done MIME crap and we do not want to add extra header
to say this is 8bit in pp_title_line();
0 : we haven't done MIME and we have not seen anything that is 8bit yet;
1 : we haven't done MIME and we have seen something that is 8bit;
pp_title_line() must add MIME header.
It adds two tests by Jeff King who independently diagnosed this issue.
Signed-off-by: Junio C Hamano <firstname.lastname@example.org>