Remove lots of numeric traits from the preludes

Num, NumCast, Unsigned, Float, Primitive and Int have been removed.

src/libsyntax/ast.rs

@@ -20,6 +20,7 @@ use ptr::P;
 
 use std::fmt;
 use std::fmt::Show;
+use std::num::Int;
 use std::rc::Rc;
 use serialize::{Encodable, Decodable, Encoder, Decoder};