This patch is to correct the manipulation of signal masks when
installing signal handlers for lxc-init. 
Signed-off-by: Jian Xiao <jian@linux.vnet.ibm.com>
Signed-off-by: Greg Kurz <gkurz@fr.ibm.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>