restorer: Switch restoring of /proc/pid/exe symlink to new kernel interface

This patch makes crtools to work with new /proc/pid/exe symlink
restoration (the kernel part was reviewed by Oleg).

So this patch is for new shiny kernel only (!), thus I suggest
all developers to move on kernel crtools-3.3 (which can be
found at usual place) and pick up this patch for crtools itself.

(again, with this patch anything but crtools-3.3 will not work)

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>