Small corrections when setting 'L->top'

- OP_NEWTABLE can use 'ra + 1' to set top (instead of ci->top);
- OP_CLOSE doesn't need to set top ('Protect' already does that);
- OP_TFORCALL must use 'ProtectNT', to preserve the top already set.
  (That was a small bug, because iterators could be called with
   extra parameters besides the state and the control variable.)
- Comments and an extra test for the bug in previous item.
4 files changed