auto merge of #5696 : thestinger/rust/hashmap, r=sanxiyn

This naming is free now that `oldmap` has finally been removed, so this is a search-and-replace to take advantage of that. It might as well be called `HashMap` instead of being named after the specific implementation, since there's only one.

SipHash distributes keys so well that I don't think there will ever be much need to use anything but a simple hash table with open addressing. If there *is* a better way to do it, it will probably be better in all cases and can just be the default implementation. 

A cuckoo-hashing implementation combining a weaker hash with SipHash could be useful, but that won't be as general purpose - you would need to write a separate fast hash function specialized for the type to really take advantage of it (like taking a page from libstdc++/libc++ and just using the integer value as the "hash"). I think a more specific naming for a truly alternative implementation like that would be fine, with the nice naming reserved for the general purpose container.

doc/rust.md

@@ -441,10 +441,10 @@ expression context, the final namespace qualifier is omitted.
 Two examples of paths with type arguments:
 
 ~~~~
-# use core::hashmap::linear::LinearMap;
+# use core::hashmap::HashMap;
 # fn f() {
 # fn id<T:Copy>(t: T) -> T { t }
-type t = LinearMap<int,~str>;  // Type arguments used in a type expression
+type t = HashMap<int,~str>;  // Type arguments used in a type expression
 let x = id::<int>(10);         // Type arguments used in a call expression
 # }
 ~~~~

doc/tutorial.md

@@ -1888,8 +1888,8 @@ illegal to copy and pass by value.
 Generic `type`, `struct`, and `enum` declarations follow the same pattern:
 
 ~~~~
-# use core::hashmap::linear::LinearMap;
-type Set<T> = LinearMap<T, ()>;
+# use core::hashmap::HashMap;
+type Set<T> = HashMap<T, ()>;
 
 struct Stack<T> {
     elements: ~[T]

src/libcore/gc.rs

@@ -43,7 +43,7 @@ use io;
 use libc::{size_t, uintptr_t};
 use option::{None, Option, Some};
 use ptr;
-use hashmap::linear::LinearSet;
+use hashmap::HashSet;
 use stackwalk;
 use sys;
 
@@ -344,7 +344,7 @@ pub fn cleanup_stack_for_failure() {
             ptr::null()
         };
 
-        let mut roots = LinearSet::new();
+        let mut roots = HashSet::new();
         for walk_gc_roots(need_cleanup, sentinel) |root, tydesc| {
             // Track roots to avoid double frees.
             if roots.contains(&*root) {