added tests for assignable and memory

tests/sprint2/test/test_invalid_release.alpha

@@ -0,0 +1,8 @@
+type rec: [integer: x; integer: y]
+
+entry(arg) := {
+	   [rec: w]
+	   w := reserve w;
+	   w := release (w);
+	   return 0;
+}