[OFBiz] Dev - product content wrapper caching

[Si Chen]

David,

I noticed you removed the product content caching in the 
ProductContentWrapper.  You said it needs to do "auto cache clear".  Can 
you explain what needs to be done to do the caching correctly? 

This was my patch originally, and it's really improved the performance 
on our site.  I'd like to make sure that we're doing it correctly.  Also 
if anybody else needs it, it'd be nice if it's in the code base.

Thanks,

Si