Allow ObjectCollections->toArray() to serialise without foreign objects.

[kitsunde]

The default for ObjectCollections->toArray() was also to always serialise foreign objects. But the default for Model->toArray() was to not serialise foreign objects. I've put the ObjectCollections->toArray() to not serialise foreign objects by default to keep the API consistent.

[marcj]

Guess it would be better to make the default to true or at least adjust all failing tests 😄