added tests for assignable and memory

tests/sprint2/test/test_valid_assignable_and_mem.alpha

@@ -0,0 +1,12 @@
+type rec: [integer: x; integer: y]
+type T2: rec -> integer
+
+entry(arg) := {
+        [rec: w]
+	w := reserve w;
+	w.x := 1;
+	w.y := 2;
+	w := release w;
+	return 0;
+        
+}