fix a logic bug in small_bitv.set

src/libstd/bitv.rs

@@ -61,7 +61,7 @@ struct small_bitv {
             self.bits |= 1<<i;
         }
         else {
-            self.bits &= !(i as u32);
+            self.bits &= !(1<<i as u32);
         }
     }
     #[inline(always)]
@@ -456,6 +456,14 @@ mod tests {
         assert act.eq_vec(~[1u]);
     }
 
+    #[test]
+    fn test_2_elements() {
+        let b = bitv::bitv(2, false);
+        b.set(0, true);
+        b.set(1, false);
+        assert b.to_str() == ~"10";
+    }
+
     #[test]
     fn test_10_elements() {
         let mut act;