added lox test files

lox.t/closure/reuse_closure_slot.lox

@@ -0,0 +1,16 @@
+{
+  var f;
+
+  {
+    var a = "a";
+    fun f_() { print a; }
+    f = f_;
+  }
+
+  {
+    // Since a is out of scope, the local slot will be reused by b. Make sure
+    // that f still closes over a.
+    var b = "b";
+    f(); // expect: a
+  }
+}