Mark the rest of the unicode feature flag as perma-unstable.

src/liballoc/lib.rs

@@ -113,7 +113,7 @@
 #![feature(trusted_len)]
 #![feature(try_reserve)]
 #![feature(unboxed_closures)]
-#![feature(unicode)]
+#![feature(unicode_internals)]
 #![feature(unsize)]
 #![feature(allocator_internals)]
 #![feature(on_unimplemented)]