thunderbird-patch-inline: avoid bashism

The use of "echo -e" is not portable and not specified by POSIX.  dash
does not support any options except "-n", and so this script will not
work on operating systems which use that as /bin/sh.

Fortunately, the solution is easy: switch to printf(1), which is
specified by POSIX and allows the escape sequences we want to use.  This
will allow the script to work with any POSIX shell.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: bk2204

contrib/thunderbird-patch-inline/appp.sh

@@ -31,7 +31,7 @@ BODY=$(sed -e "1,/${SEP}/d" $1)
 CMT_MSG=$(sed -e '1,/^$/d' -e '/^---$/,$d' "${PATCH}")
 DIFF=$(sed -e '1,/^---$/d' "${PATCH}")
 
-CCS=$(echo -e "$CMT_MSG\n$HEADERS" | sed -n -e 's/^Cc: \(.*\)$/\1,/gp' \
+CCS=$(printf '%s\n%s\n' "$CMT_MSG" "$HEADERS" | sed -n -e 's/^Cc: \(.*\)$/\1,/gp' \
 	-e 's/^Signed-off-by: \(.*\)/\1,/gp')
 
 echo "$SUBJECT" > $1