lua: update to version 5.2

lua: update to version 5.2

- Update to support the new behavior of varargs and table.pack/unpack
  in lua 5.2
- Bump up the stack overflow test since lua 5.2 seems to support much
  larger stacks before overflow.
- Fix a latent issue in if forms where false in the 4th position would
  result in nil returned. Add a new test to catch this in the future.