[Checkers] nonnull & interned demos in SVN

[Matt Papi]

I added the demos for NonNull and Interned to 
annotations/demos/nonnull-interned-demo. See the README in that 
directory for more info.

(I committed more files than should be necessary because demos depend on 
specific versions of those files; eventually I will either prune them or 
specify how to obtain the correct versions. For now I simply wanted to 
start with something that has been demoed twice without any problems.)


- Matt