Fix fallout from coercion removal

src/libstd/num/uint_macros.rs

@@ -38,7 +38,7 @@ pub fn to_str_bytes<U>(n: $T, radix: uint, f: |v: &[u8]| -> U) -> U {
     // base 2 number, and then we need another for a possible '-' character.
     let mut buf = [0u8, ..65];
     let amt = {
-        let mut wr = ::io::BufWriter::new(buf);
+        let mut wr = ::io::BufWriter::new(&mut buf);
         (write!(&mut wr, "{}", ::fmt::radix(n, radix as u8))).unwrap();
         wr.tell().unwrap() as uint
     };