packet_write_fmt_gently() uses format_packet() which lets the caller
only send string data via "%s". That means it cannot be used for
arbitrary data that may contain NULs.
Add packet_write_gently() which writes arbitrary data and does not die
in case of an error. The function is used by other pkt-line functions in
a subsequent patch.
Signed-off-by: Lars Schneider <larsxschneider@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>