[Developers] Refactoring /automotive/manufacturing_plant/generations_built

[Bryan Cheung]

A request in this discussion post:

http://www.freebase.com/view/guid/9202a8c04000641f8000000009d87c52

has turned into this refactoring task:

https://bugs.freebase.com/browse/DA-507

To summarize, the data for car generations manufactured at a  
manufacturing plant will be refactored into a time mediated CVT, and  
then the property /automotive/manufacturing_plant/generations_built  
will be deleted.

I've modeled this on sandbox:

http://sandbox.freebase.com/type/schema/automotive/manufacturing_plant_model_relationship

Any applications that expect  /automotive/manufacturing_plant/ 
generations_built will break and should be updated.  I'd like to make  
this change shortly (by the end of the week, if not sooner); if there  
is anyone that is adversely affected by this change, speak up and we  
can work on the timing.

Thanks,
Bryan