pbx_lua: Add support for Lua 5.2

This adds support for Lua 5.2 in pbx_lua which is available on newer
operating systems.

(closes issue ASTERISK-23011)
Review: https://reviewboard.asterisk.org/r/3075/
Reported by: George Joseph
Patch by: George Joseph
........

Merged revisions 405090 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@405091 65c4cc65-6c06-0410-ace0-fbb531ad65f3