Set unstable feature names appropriately

* `core` - for the core crate
* `hash` - hashing
* `io` - io
* `path` - path
* `alloc` - alloc crate
* `rand` - rand crate
* `collections` - collections crate
* `std_misc` - other parts of std
* `test` - test crate
* `rustc_private` - everything else

src/libstd/sys/unix/ext.rs

@@ -29,7 +29,7 @@
 //! }
 //! ```
 
-#![unstable(feature = "unnamed_feature")]
+#![unstable(feature = "std_misc")]
 
 use sys_common::AsInner;
 use libc;