Rust updates

[Walter Bright]

On 7/11/2012 11:54 AM, David Piepgrass wrote:
> That reminds me, I was so happy the first two times I got an undefined symbol
> error in D. The compiler said: "Did you mean '<correct variable name>'?" LOL,
> don't tell me how it works... it's magic, right? I love a good error message.

I added a spelling checker to the undefined identifier code, using the variables 
in scope as the dictionary. It's a fun little nicety.