libcore: Remove mutable fields from rand.

Author: pcwalton

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();
+    let mut r = rand::task_rng();
     linear_map_with_capacity_and_keys(r.gen(), r.gen(),
                                       initial_capacity)
 }