Mark Unique as perma-unstable, with the feature renamed to ptr_internals.

src/liballoc/lib.rs

@@ -110,6 +110,7 @@
 #![feature(pattern)]
 #![feature(placement_in_syntax)]
 #![feature(placement_new_protocol)]
+#![feature(ptr_internals)]
 #![feature(rustc_attrs)]
 #![feature(slice_get_slice)]
 #![feature(slice_patterns)]
@@ -120,7 +121,6 @@
 #![feature(trusted_len)]
 #![feature(unboxed_closures)]
 #![feature(unicode)]
-#![feature(unique)]
 #![feature(unsize)]
 #![feature(allocator_internals)]
 #![feature(on_unimplemented)]