auto merge of #12017 : FlaPer87/rust/replace-mod-crate, r=alexcrichton

The first setp for #9880 is to add a new `crate` keyword. This PR does exactly that. I took a chance to refactor `parse_item_foreign_mod` and I broke it down into 2 separate methods to isolate each feature.

The next step will be to push a new stage0 snapshot and then get rid of all `extern mod` around the code.

src/test/compile-fail/extern-expected-fn-or-brace.rs

@@ -0,0 +1,14 @@
+// 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.
+
+// Verifies that the expected token errors for `extern crate` are
+// raised
+
+extern "C" mod foo; //~ERROR expected `{` or `fn` but found `mod`

src/test/compile-fail/extern-foreign-crate.rs

@@ -0,0 +1,14 @@
+// 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.
+
+// Verifies that the expected token errors for `extern crate` are
+// raised
+
+extern crate foo {} //~ERROR expected one of `=`, `;` but found `{`

src/test/compile-fail/obsolete-syntax.rs

@@ -8,11 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-extern mod obsolete_name {
-    //~^ ERROR obsolete syntax: named external module
-    fn bar();
-}
-
 trait A {
     pub fn foo(); //~ ERROR: visibility not necessary
     pub fn bar(); //~ ERROR: visibility not necessary

src/test/run-pass/extern-foreign-crate.rs

@@ -0,0 +1,14 @@
+// Copyright 2013 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.
+
+extern crate extra;
+extern mod mystd = "std";
+
+pub fn main() {}