Add tests that the injected runtime is inaccessible

src/test/compile-fail/hidden-rt-injection.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// This is testing that users can't access the runtime crate.
+
+mod m {
+    // The rt has been called both 'native' and 'rt'
+    use native; //~ ERROR unresolved import
+}
+
+fn main() { }

src/test/compile-fail/hidden-rt-injection2.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// This is testing that users can't access the runtime crate.
+
+mod m {
+    // The rt has been called both 'native' and 'rt'
+    use rt; //~ ERROR unresolved import
+}
+
+fn main() { }