Fix logic error in Vector::ptr_eq

I believe the intent of this code was to consider the last two
operations as a single OR. (I may be wrong)

- closes bodil#131

src/vector/mod.rs

@@ -347,8 +347,8 @@ impl<A: Clone> Vector<A> {
                     && cmp_chunk(&left.inner_f, &right.inner_f)
                     && cmp_chunk(&left.inner_b, &right.inner_b)
                     && cmp_chunk(&left.outer_b, &right.outer_b)
-                    && (left.middle.is_empty() && right.middle.is_empty())
-                    || Ref::ptr_eq(&left.middle, &right.middle)
+                    && ((left.middle.is_empty() && right.middle.is_empty())
+                        || Ref::ptr_eq(&left.middle, &right.middle))
             }
             _ => false,
         }
@@ -2481,6 +2481,33 @@ mod test {
         assert_eq!(vec.len(), rev_vec.len());
     }
 
+    #[test]
+    fn issue_131() {
+        let smol = std::iter::repeat(42).take(64).collect::<Vector<_>>();
+        let mut smol2 = smol.clone();
+        assert!(smol.ptr_eq(&smol2));
+        smol2.set(63, 420);
+        assert!(!smol.ptr_eq(&smol2));
+
+        let huge = std::iter::repeat(42).take(65).collect::<Vector<_>>();
+        let mut huge2 = huge.clone();
+        assert!(huge.ptr_eq(&huge2));
+        huge2.set(63, 420);
+        assert!(!huge.ptr_eq(&huge2));
+    }
+
+    #[test]
+    fn ptr_eq() {
+        for len in 32..256 {
+            let input = std::iter::repeat(42).take(len).collect::<Vector<_>>();
+            let mut inp2 = input.clone();
+            assert!(input.ptr_eq(&inp2));
+            inp2.set(len-1, 98);
+            assert_ne!(inp2.get(len-1), input.get(len-1));
+            assert!(!input.ptr_eq(&inp2), len);
+        }
+    }
+
     proptest! {
         #[test]
         fn iter(ref vec in vec(i32::ANY, 0..1000)) {