[Cronometer-development] diffSource

[Aaron D. <ada...@po...>]

Right now it can't create new foods as it complains in diffSource() 
that the source is the same. I think this was intended to prevent 
adding a food that already exists in the mutable foods.

How should we handle this case? Should I modify diffSource() to 
actually query the source for the prior existence of the food, or 
should I work higher up the call hierarchy to avoid calling 
diffSource() when adding a new food?