It has only one user. Also, in next patches will be
used pstree_item_by_virt() function, and I don't
want to add "#include" to "files.h" for it, and to
nest headers.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>