Merge the Bitwise and ByteOrder traits into the Int trait

This reduces the complexity of the trait hierarchy.

src/test/bench/sudoku.rs

@@ -16,7 +16,6 @@
 use std::io;
 use std::io::stdio::StdReader;
 use std::io::BufferedReader;
-use std::num::Bitwise;
 use std::os;
 
 // Computes a single solution to a given 9x9 sudoku