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/libcore/lib.rs

@@ -48,7 +48,7 @@
 // separate crate, libcoretest, to avoid bizarre issues.
 
 #![crate_name = "core"]
-#![unstable(feature = "unnamed_feature")]
+#![unstable(feature = "core")]
 #![feature(staged_api)]
 #![staged_api]
 #![crate_type = "rlib"]