Make `User`'s equality depend on its `UserID`

sources/Users/User.uc

@@ -176,6 +176,22 @@ public final function bool SetPersistentData(
     return result;
 }
 
+public function bool IsEqual(Object other) {
+    local User otherUser;
+
+    if (id == none)             return false;
+    otherUser = User(other);
+    if (otherUser == none)      return false;
+    if (otherUser.id == none)   return false;
+
+    return id.IsEqual(otherUser.id);
+}
+
+protected function int CalculateHashCode() {
+    // If `id` is `none`, then caller `User` shouldn't be used at all
+    return id.GetHashCode();
+}
+
 defaultproperties
 {
 }