Provide a more meaningful initial "From " line when using --compose in git-send-email.

Provide a more meaningful initial "From " line when using --compose in git-send-email.

git-send-email, when used with --compose, provided the user with a mbox-format
file to edit.  Some users, however, were confused by the leading, blank, "From
" line, so this change puts the value that will appear on the From: line of the
actual email on this line, along with a note that the line is ignored.

Signed-off-by: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>