Lua: improve level testing

Add des.finalize_level() used for testing in conjunction with
des.reset_level().
Add nhc.DLB to return 0 or 1 if DLB was defined at compile-time.
Change the test_lev.lua to give more informative messages instead of
just lua error when required file doesn't exist.
Add bigrm-11 to the level tests.

src/nhlua.c

@@ -976,6 +976,11 @@ static const struct {
 } nhl_consts[] = {
     { "COLNO",  COLNO },
     { "ROWNO",  ROWNO },
+#ifdef DLB
+    { "DLB", 1},
+#else
+    { "DLB", 0},
+#endif /* DLB */
     { NULL, 0 },
 };