Bad error message dereferencing something with a class type

[catamorphism]

class cat { new() {} }

fn main() {
  log (error, *(cat()));     // 1
  let nyan = cat();
  log (error, *nyan);       // 2
  let kitty : cat = cat();
  log (error, *kitty);        // 3
}

(1) yields the correct error message: "Type cat cannot be dereferenced". (2) and (3) yield less-than-helpful error messages of the form "Type <V1> cannot be dereferenced".

[nikomatsakis]

I happen to have fixed for this in the borrowck code, which I'll hopefully push soon... but basically we should be using fcx.to_str(ty) not ty_to_str(tcx, ty)