Generate code into OUT_DIR.

This is necessary to ensure Cargo knows when to rebuild. Normally
.gitignore would be enough to exclude these from Cargo's freshness
calculation, but https://github.com/rust-lang/cargo/issues/1729 prevents
this currently. This is the new, correct way to do these thigns, just
like the style crate does.

components/script/dom/mod.rs

@@ -190,8 +190,9 @@ pub mod macros;
 
 pub mod bindings;
 
-#[path="bindings/codegen/InterfaceTypes.rs"]
-pub mod types;
+pub mod types {
+    include!(concat!(env!("OUT_DIR"), "/InterfaceTypes.rs"));
+}
 
 pub mod activation;
 pub mod attr;