std: rewrite Hash to make it more generic

This patch merges IterBytes and Hash traits, which clears up the
confusion of using `#[deriving(IterBytes)]` to support hashing.
Instead, it now is much easier to use the new `#[deriving(Hash)]`
for making a type hashable with a stream hash.

Furthermore, it supports custom non-stream-based hashers, such as
if a value's hash was cached in a database.

This does not yet replace the old IterBytes-hash with this new
version.

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;

src/librustc/metadata/decoder.rs

@@ -27,6 +27,7 @@ use middle::typeck;
 use middle::astencode::vtable_decoder_helpers;
 
 use std::u64;
+use std::hash_old::Hash;
 use std::io;
 use std::io::extensions::u64_from_be_bytes;
 use std::option;

src/librustc/metadata/encoder.rs

@@ -26,6 +26,7 @@ use middle;
 use serialize::Encodable;
 use std::cast;
 use std::cell::{Cell, RefCell};
+use std::hash_old::Hash;
 use std::hashmap::{HashMap, HashSet};
 use std::io::MemWriter;
 use std::str;

src/librustc/middle/ty.rs

@@ -4916,7 +4916,7 @@ pub fn trait_method_of_method(tcx: ctxt,
 /// Creates a hash of the type `t` which will be the same no matter what crate
 /// context it's calculated within. This is used by the `type_id` intrinsic.
 pub fn hash_crate_independent(tcx: ctxt, t: t, local_hash: ~str) -> u64 {
-    use std::hash::{SipState, Streaming};
+    use std::hash_old::{SipState, Streaming};
 
     let mut hash = SipState::new(0, 0);
     let region = |_hash: &mut SipState, r: Region| {

src/libserialize/serialize.rs

@@ -14,6 +14,7 @@
 Core encoding and decoding interfaces.
 */
 
+use std::hash_old::Hash;
 use std::hashmap::{HashMap, HashSet};
 use std::rc::Rc;
 use std::trie::{TrieMap, TrieSet};