/proc/PID/maps can contains not up to date information about a stack vma.
A kernel marks a VMA as stack, if thread_struct->usersp is in it,
but usersp is updated, when a process calls a syscall.

This problem is occured, when we try to dump/restore a process in a loop.
When a restorer resumes a process, a restorer vma will be marked as stack.

A thread stack should not be marked as stack, because its vma is mapped
w/o MAP_GROWSDOWN.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>