Rename macro_escape to macro_use

In the future we want to support

    #[macro_use(foo, bar)]
    mod macros;

but it's not an essential part of macro reform.  Reserve the syntax for now.

src/libstd/io/mod.rs

@@ -285,7 +285,8 @@ pub mod stdio;
 pub mod timer;
 pub mod util;
 
-#[macro_escape]
+#[cfg_attr(stage0, macro_escape)]
+#[cfg_attr(not(stage0), macro_use)]
 pub mod test;
 
 /// The default buffer size for various I/O operations