auto merge of #13295 : huonw/rust/gate-concat-idents, r=alexcrichton

rustc: feature-gate `concat_idents!`.

concat_idents! is not as useful as it could be, due to macros only being
allowed in limited places, and hygiene, so lets feature gate it until we
make a decision about it.

cc #13294

diff --combined src/libstd/lib.rs
index 5177bc08890b6f01f941cc886d0f085ef2d621ee,b1cf4cf7d566b708d894f2fd58193214eb88128b..f4f5be4d37a46f9e3d5e98701c562a77621a3f98
--- 1/src/libstd/lib.rs
--- 2/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@@ -43,7 -43,7 +43,7 @@@
  //!
  //!     use std::prelude::*;
  
 -#![crate_id = "std#0.10"]
 +#![crate_id = "std#0.11-pre"]
  #![comment = "The Rust standard library"]
  #![license = "MIT/ASL2"]
  #![crate_type = "rlib"]
@@@ -52,7 -52,7 +52,7 @@@
         html_favicon_url = "http://www.rust-lang.org/favicon.ico",
         html_root_url = "http://static.rust-lang.org/doc/master")]
  #![feature(macro_rules, globs, asm, managed_boxes, thread_local, link_args,
-            simd, linkage, default_type_params, phase)]
+            simd, linkage, default_type_params, phase, concat_idents)]
  
  // Don't link to std. We are std.
  #![no_std]
@@@ -60,6 -60,7 +60,7 @@@
  // #![deny(missing_doc)] // NOTE: uncomment after a stage0 snap
  #![allow(missing_doc)] // NOTE: remove after a stage0 snap
  #![allow(visible_private_types)] // NOTE: remove after a stage0 snap
+ #![allow(unknown_features)] // NOTE: remove after a stage0 snap
  
  // When testing libstd, bring in libuv as the I/O backend so tests can print
  // things and all of the std::io tests have an I/O interface to run on top
@@@ -232,5 -233,4 +233,5 @@@ mod std 
      pub use to_str;
      pub use ty;
      pub use unstable;
 +    pub use vec;
  }