Use new attribute syntax in python files in src/etc too (rust-lang#13478)

Author: Manishearth

src/etc/generate-deriving-span-tests.py

@@ -37,7 +37,7 @@
 
 // This file was auto-generated using 'src/etc/generate-keyword-span-tests.py'
 
-#[feature(struct_variant)];
+#![feature(struct_variant)]
 extern crate rand;
 
 {error_deriving}

src/etc/unicode.py

@@ -411,8 +411,8 @@ def emit_decomp_module(f, canon, compat, combine):
 
 // The following code was generated by "src/etc/unicode.py"
 
-#[allow(missing_doc)];
-#[allow(non_uppercase_statics)];
+#![allow(missing_doc)]
+#![allow(non_uppercase_statics)]
 
 ''')