Handle cases where relationship is UnsavedRelationList

[monkeyfeet]

When saving a DO, type error is thrown if one of the relationships is an UnsavedRalationList (expects DataList). This change introduces a check for instance of DataList before processing the relations.

[chrispenny]

After some discussion, we were a little unclear when/what triggers an UnsavedRelationList to be used. We initially attempted to add a condition to not process lists that were not specifically a DataList, but this seemed to have issues with our tests (and perhaps the way that fixtures scaffold records?).

It seems like a reasonable solution would be to loosen the requirement on updateInstances() to allow any type of SS_List (includes DataList, ArrayList, and UnsavedRelationList), and to instead make sure that all records are inDB() as part of the processInstance() method.