Make git-send-email detect mbox-style patches more readily
Earlier we insisted that mbox file to begin with "From ". That
is fine as long as you feed format-patch output, but if you
handcraft the input file, this is unnecessary burden. We should
detect lines that look like e-mail headers and say that is also
a mbox file.
The other input file format is traditional "send lots of email",
whose first line would never look like e-mail headers, so this
is a safe change.
The original patch was done by Matthew Wilcox, which checked
explicitly for headers the script pays attention to.
Signed-off-by: Junio C Hamano <junkio@cox.net>