Fixed $.Model.restore(true) overwriting associated (nested) models with plain objects

[marnusw]

Currently when backup/restore is used to restore a model with the restoreAssociations option the nested model is lost because it is overwritten by the plain object from the store. I propose checking whether the current property is a nested model and in that case setting its values with its own attrs() method. This preserves the nested model and also causes it to trigger the appropriate update events etc.

Two things though:

• I'm not sure whether it's OK to return early after setting the nested model values, but it seems to me that the nested model will handle everything that's necessary.
• There may be a better way to test whether a property is a nested model.