[BZ#774684] json_from_string() returns nodes with dangling parent pointers
Submitted by Ole André Vadla Ravnås <<ole..@..com>>
This is because it uses json_node_copy(), which does not copy the children of complex data types -- it only refs them. This means that the children's
parentpointers will point to the node that was copied, which might have been freed. This is always the case with json_from_string(), as it lets go of the last reference to the root node before returning the copy, which at that time has dangling parent pointers in its children.