signal: fix logig about SIGMAX (v2)

A value of signo is in [1, SIGMAX].
Currenly signals are enumirated from 1 to SIGMAX, but SIGMAX
is not included. This patch fixes this mestake.

v2: * save backward compatibility
    * set a correct value of SIGMAX = 64. It can not be in a
    separate patch, because a format is changed again.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>