[Rivet] Updated Cuts system prototype/demo

[David Grellscheid]

Hi Andy,

> references are taken w.r.t. stack-allocated temporaries passed to
> their constructors: I don't understand why this isn't as doomed to
> failure as taking a pointer to a temporary? I suspect there is a
> facet of C++ object lifetimes here that I don't/didn't appreciate!

Damn. I knew I missed something there. A _local_ const reference to a
temporary (all examples in main() are like that) keeps the temporary
alive until all refs are gone, but that does not work across scopes. A
slightly more indirect main function (e.g. set c3 with a function call)
breaks for the reason you mentioned. It'll have to go back to smart_ptr
or auto. Hmmm.

At least in C++11 you won't need boost: all the functions
you're using are in standard C++11.

> need to be set by the constructor initialization list

References don't have to be const, but must be set in the constructor.
They cannot be re-pointed elsewhere. Assigning to the reference member 
later on changes the original object, it does not re-point the reference 
to something else.

   David