Check that files opened before switching to new mount namespace
remain in it after restore. Right now this is not so :( Andrey is
fixing the issue.

Christopher, can you check whether the ns_child's call to system()
works in your minimal set-ups (it launches cat and awk). If not,
then I should rewrite this routine in pure C.

The first version was written by Pavel (xemul@).

v2: don't use test_init_ns
    don't call awk and cat
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>