Update libcollections tests to pass the new type rules. They used to …

…return a pointer to the value they were modifying, but this should not have been legal, since that pointer would have to outlive the closure, and the closure continues to modify the value during the execution. This return value was just passed to `black_box` so as to convince llvm that the value was live, so rather than returning a pointer, modify to just call `black_box` directly inside the fn.

src/libcollections/bit.rs

@@ -1678,10 +1678,10 @@ impl<'a> Iterator<uint> for TwoBitPositions<'a> {
 mod tests {
     use std::prelude::*;
     use std::iter::range_step;
-    use std::u32;
     use std::rand;
     use std::rand::Rng;
-    use test::Bencher;
+    use std::u32;
+    use test::{Bencher, black_box};
 
     use super::{Bitv, BitvSet, from_fn, from_bytes};
     use bitv;
@@ -2676,8 +2676,8 @@ mod tests {
             for _ in range(0u, 100) {
                 bitv |= 1 << ((r.next_u32() as uint) % u32::BITS);
             }
-            &bitv
-        })
+            black_box(&bitv)
+        });
     }
 
     #[bench]
@@ -2688,8 +2688,8 @@ mod tests {
             for _ in range(0u, 100) {
                 bitv.set((r.next_u32() as uint) % BENCH_BITS, true);
             }
-            &bitv
-        })
+            black_box(&bitv)
+        });
     }
 
     #[bench]
@@ -2700,8 +2700,8 @@ mod tests {
             for _ in range(0u, 100) {
                 bitv.set((r.next_u32() as uint) % BENCH_BITS, r.gen());
             }
-            &bitv
-        })
+            black_box(&bitv);
+        });
     }
 
     #[bench]
@@ -2712,8 +2712,8 @@ mod tests {
             for _ in range(0u, 100) {
                 bitv.set((r.next_u32() as uint) % u32::BITS, true);
             }
-            &bitv
-        })
+            black_box(&bitv);
+        });
     }
 
     #[bench]
@@ -2724,8 +2724,8 @@ mod tests {
             for _ in range(0u, 100) {
                 bitv.insert((r.next_u32() as uint) % u32::BITS);
             }
-            &bitv
-        })
+            black_box(&bitv);
+        });
     }
 
     #[bench]
@@ -2736,8 +2736,8 @@ mod tests {
             for _ in range(0u, 100) {
                 bitv.insert((r.next_u32() as uint) % BENCH_BITS);
             }
-            &bitv
-        })
+            black_box(&bitv);
+        });
     }
 
     #[bench]

src/libcollections/slice.rs

@@ -2084,7 +2084,7 @@ mod bench {
     use std::rand::{weak_rng, Rng};
     use std::mem;
     use std::ptr;
-    use test::Bencher;
+    use test::{Bencher, black_box};
 
     use vec::Vec;
 
@@ -2140,8 +2140,8 @@ mod bench {
         let mut vec: Vec<uint> = vec![];
         b.iter(|| {
             vec.push(0);
-            &vec
-        })
+            black_box(&vec);
+        });
     }
 
     #[bench]