auto merge of #6036 : huonw/rust/core-less-at, r=nikomatsakis

From a cursory `git grep` this removes the last part of `core` that requires on `@` (other than `io` and the task local data section).

It renames `RandRes` to ~~StdRng~~ `IsaacRng` and `XorShiftState` to `XorShiftRng` as well as moving their constructors to static methods. To go with this, it adds `rng()` which is designed to be used when the programmer just wants a random number generator, without caring about which exact algorithm is being used.

It also removes all the `gen_int`, `gen_uint`, `gen_char` (etc) methods on `RngUtil` (by moving the defintions to the actual `Rand` instances). The replacement is using `RngUtil::gen`, either type-inferred or with an annotation (`rng.gen::<uint>()`).

I tried to have the `Rng` and `RngUtil` traits exported by `core::prelude` (since `core::rand` (except for `random()`) is useless without them), but this caused [an explosion of (seemingly unrelated) `error: unresolved import`'s](https://gist.github.com/5451839).

Author: bors

src/libcore/flate.rs

@@ -85,7 +85,7 @@ pub fn inflate_bytes(bytes: &const [u8]) -> ~[u8] {
 #[test]
 #[allow(non_implicitly_copyable_typarams)]
 fn test_flate_round_trip() {
-    let r = rand::Rng();
+    let r = rand::rng();
     let mut words = ~[];
     for 20.times {
         words.push(r.gen_bytes(r.gen_uint_range(1, 10)));

src/libcore/hashmap.rs

@@ -56,7 +56,7 @@ fn resize_at(capacity: uint) -> uint {
 pub fn linear_map_with_capacity<K:Eq + Hash,V>(
     initial_capacity: uint) -> HashMap<K, V> {
     let r = rand::task_rng();
-    linear_map_with_capacity_and_keys(r.gen_u64(), r.gen_u64(),
+    linear_map_with_capacity_and_keys(r.gen(), r.gen(),
                                       initial_capacity)
 }
 

src/libcore/os.rs

@@ -1259,7 +1259,7 @@ mod tests {
     }
 
     fn make_rand_name() -> ~str {
-        let rng: @rand::Rng = rand::Rng();
+        let rng = rand::rng();
         let n = ~"TEST" + rng.gen_str(10u);
         assert!(getenv(n).is_none());
         n