We use two commands to get task registers safely. The first command
blocked signals, then crtools dumped registers and all per-thread data
and the the second command unblocks signals.

Currently signals can be blocked with help SETSIGMASK, so we need only
one command to dump per-thread data.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>