This patch adds ability to checkpoint/restore
/proc/pid/exe symlink, so if a process we've just
checkpointed has been say /path/to/exe, then at restore
time we bring this path back.

There some restiction from kernel side: if
existing /proc/pid/exe already mapped more than
once, the kernel will refuse to change the symlink,
so we need to restore it lately when mmaps of crtools
itself already unmapped (ie via late call in
restorer.c).
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>