rustc_resolve: don't handle impl items as if they were modules.

src/test/compile-fail/impl-duplicate-methods.rs

@@ -11,7 +11,7 @@
 struct Foo;
 impl Foo {
     fn orange(&self){}
-    fn orange(&self){}   //~ ERROR error: duplicate definition of value `orange`
+    fn orange(&self){}   //~ ERROR error: duplicate method in trait impl
 }
 
 fn main() {}