= paperclipped_multi_site

This extension scopes assets to sites. Our fork of multi-site is needed, and does most of the work in the model (by 
putting a scope around find, essentially), so there are no controller modifications required and we can shrink this to a 
couple of lines.

You could probably get rid of this extension altogether by adding this to Asset:

  is_site_scoped if defined? Site && Radiant::Config['assets.scoped?']

But the conditionality does make your tests a bit more tangled.

Some basic tests are included to make sure that Asset loads and is properly scoped.