[WIP] cascade insert does not work with autoname

Test to demonstrate #388 , the id strategy is ignored in cascading the insert.

The first test shows that adding a document in a children collection of an already persisted document works, but persisting a new document with children does not. This is rather strange, as i would expect the children persisting to go through the same code path.

I won't have time to investigate further until next week, so if somebody could pick this up, would be great.