lib: talloc: Allow destructors to reparent the object they're called on.

lib: talloc: Allow destructors to reparent the object they're called on.

If a destructor returns failure (-1) when freeing a child, talloc
must then reparent the child.

Firstly it tries the owner of any reference, next the parent of the
current object calling _talloc_free_children_internal(), and finally
the null context in the last resort.

If a destructor reparented its own object, which can be a very
desirable thing to do (a destructor can make a decision it isn't
time to die yet, and as the parent may be going away it might
want to move itself to longer-term storage) then this new parent
gets overwritten by the existing reparenting logic.

This patch checks when freeing a child if it already reparented
itself, and if it did doesn't then overwrite the new parent.

Makes destructors more flexible.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Ira Cooper <ira@samba.org>