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/path/mod.rs

@@ -59,7 +59,7 @@
 //! println!("path exists: {}", path.exists());
 //! ```
 
-#![unstable(feature = "unnamed_feature")]
+#![unstable(feature = "path")]
 
 use core::marker::Sized;
 use ffi::CString;