Fix zone_allocator to support comparison

src/zone-allocator.h

Index: src/zone-allocator.h
diff --git a/src/zone-allocator.h b/src/zone-allocator.h
index 5245c6b1bfd45d3d23e5e5efb82a5b4fa4707fba..312d395c8379af143dcaafd530d3c9b58a6e657f 100644
--- a/src/zone-allocator.h
+++ b/src/zone-allocator.h
@@ -69,7 +69,14 @@ class zone_allocator {
   void construct(pointer p, const T& val) {
     new(static_cast<void*>(p)) T(val);
   }
-  void destroy(pointer p) { (static_cast<T*>(p))->~T(); }
+  void destroy(pointer p) { p->~T(); }
+
+  bool operator==(zone_allocator const& other) {
+    return zone_ == other.zone_;
+  }
+  bool operator!=(zone_allocator const& other) {
+    return zone_ != other.zone_;
+  }
 
  private:
   Zone* zone_;