dump: Check for pids reuse at suspend

While we try to seize task it can die and give its pid to
somebody else. This can break pstree consistency. Check for
parent being valid after task is seized.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>

include/crtools.h

@@ -150,6 +150,7 @@ struct vma_area {
 struct pstree_item {
 	struct list_head	list;
 	pid_t			pid;		/* leader pid */
+	pid_t			ppid;
 	int			state;		/* TASK_XXX constants */
 	u32			nr_children;	/* number of children */
 	u32			nr_threads;	/* number of threads */