auto merge of #21082 : brson/rust/finally, r=alexcrichton

No in-tree users. Ugly interface. Closes #14332.

I just happened to notice that this module still lives and has no users. Assuming we don't want it.

r? @aturon cc @alexcrichton

src/libcore/finally.rs

@@ -32,7 +32,11 @@
 //! # }
 //! ```
 
-#![unstable]
+#![deprecated = "It is unclear if this module is more robust than implementing \
+                 Drop on a custom type, and this module is being removed with no \
+                 replacement. Use a custom Drop implementation to regain existing \
+                 functionality."]
+#![allow(deprecated)]
 
 use ops::{Drop, FnMut, FnOnce};