removed reference to crate file keywords
Commenting, test cases, cleanup
@mut fix
deriving-eq all over ast
finish deriving_eq in ast
use node_id for indexing in ast_to_ty_cache
deriving_eq for tokens and binops

Note that the replaced definition of equality on tokens
contains a *huge* shortcut on INTERPOLATED tokens (those
that contain ASTs), whereby any two INTERPOLATED tokens
are considered equal. This seems like a really broken
notion of equality, but it appears that the existing
test cases and the compiler don't depend on it. Niko
noticed this, BTW.

Replace long definition of Eq on tokens and binops
w
started work on enriching idents