Boost subgraph copy constructor in 1.55.0 not working properly but works well i 1.46.0

[Mayur Narkhede <mayur_narkhede@…>]

While using the boost 1.46.0, the copy constructor worked well to copy all deep level subgraphs. In this a recursive call to new subgraph is invoked while iterating over subgraphs hence it works well. But for boost 1.55.0, children iterator is used to iterate over subgraphs and as children iterator is able to iterate over only next level subgraphs, it do not perform deep copy and hence deep level subgraphs are not getting copied properly. I think children iterator should be made to iterate all deep level subgraphs so as to make it work like 1.46.0