Pending signals should be saved, so signals should be blocked.
Signals are blocked for EACH command, because a chance of destroying a
process state should be a small as possible.

At the end there will only two "trapped" commands -- to dump thread
and to start daemon in parasite, so this doesn't add significant
overheads.

If crtools is killed between two commands, a dumped process will run
continue.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>