Implement new mod import sugar

Implements RFC #168.

src/test/compile-fail/use-mod-2.rs

@@ -0,0 +1,19 @@
+// 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.
+
+mod foo {
+    use self::{mod};
+    //~^ ERROR unresolved import `self`. There is no `self` in `???`
+
+    use super::{mod};
+    //~^ ERROR unresolved import `super`. There is no `super` in `???`
+}
+
+fn main() {}

src/test/compile-fail/use-mod-3.rs

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+// 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.
+
+use foo::bar::{
+    mod //~ ERROR module `bar` is private
+};
+use foo::bar::{
+    Bar, //~ ERROR type `Bar` is inaccessible
+    //~^ NOTE module `bar` is private
+    mod //~ ERROR module `bar` is private
+};
+
+mod foo {
+    mod bar { pub type Bar = int; }
+}
+
+fn main() {}

src/test/compile-fail/use-mod.rs

@@ -0,0 +1,32 @@
+// 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.
+
+use foo::bar::{
+    mod,
+//~^ ERROR `mod` import can only appear once in the list
+    Bar,
+    mod
+//~^ NOTE another `mod` import appears here
+};
+
+use {mod};
+//~^ ERROR `mod` import can only appear in an import list with a non-empty prefix
+
+use foo::mod;
+//~^ ERROR `mod` imports are only allowed within a { } list
+
+mod foo {
+    pub mod bar {
+        pub struct Bar;
+        pub struct Baz;
+    }
+}
+
+fn main() {}