In this case private vma-s will be inherited by children,
it allows to restore copy-on-write reqions.

This code compares child and parent vma lists. If it found
two vma-s with the same start and end addresses, it decides
that the child inherites this vmas from the parent.

This code calculates a size of all private vma-s, then allocate
a memory region for all vma-s and maps them one by one. If a vma is
inherited it will be remaped to an allocated place.

As a result all vma-s will be placed in a continious memory region
and sorted by start addresses. This logic will be used for remap
vma-s to correct address.

v2: fix accoding with Pavel's comments ( clean up and simplify )
v3: simplify code and check that VMA-s are sorted
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>