auto merge of #11863 : erickt/rust/hash, r=acrichto

This PR merges `IterBytes` and `Hash` into a trait that allows for generic non-stream-based hashing. It makes use of @eddyb's default type parameter support in order to have a similar usage to the old `Hash` framework.

Fixes #8038.

Todo:

- [x] Better documentation
- [ ] Benchmark
- [ ] Parameterize `HashMap` on a `Hasher`.

Author: bors

src/etc/generate-deriving-span-tests.py

@@ -119,7 +119,8 @@ def write_file(name, string):
                               ('Clone', [], 1), ('DeepClone', ['Clone'], 1),
                               ('Eq', [], 2), ('Ord', [], 8),
                               ('TotalEq', [], 1), ('TotalOrd', ['TotalEq'], 1),
-                              ('Show', [], 1)]:
+                              ('Show', [], 1),
+                              ('Hash', [], 1)]:
     traits[trait] = (ALL, supers, errs)
 
 for (trait, (types, super_traits, error_count)) in traits.items():

src/libextra/stats.rs

@@ -11,6 +11,7 @@
 #[allow(missing_doc)];
 
 use std::cmp;
+use std::hash_old::Hash;
 use std::hashmap;
 use std::io;
 use std::mem;