mm: don't add a guard page if a prev vma grows-down too
mm: don't add a guard page if a prev vma grows-down too

The kernel logic is described in v2.6.36-rc1-161-g7798330:
"If we've split the stack vma, only the lowest one has the guard page."

https://bugzilla.openvz.org/show_bug.cgi?id=2715
Signed-off-by: Andrey Vagin <74c05afa918858348d6db8037d82fa8124870113@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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