Optional commas patch for 5.3

[Eduardo Tongson <propolice@...>]

Hello,

Might be useful for some people who bundle Lua.

https://github.com/Configi/configi/commit/c5f7354a7401a955e187a31dad3b59be3a3a279d

See the original patch for the description:
http://lua-users.org/lists/lua-l/2012-03/msg00175.html

It was originally for 5.1, fortunately that part of lparser.c didn't
change much. No failures according to the basic tests of the Lua 5.3
test suite. So far haven't encountered any problem with it. But I'd
like to know if it actually breaks anything.

All credit goes to Wolfgang P.
Cheers!