Import lua filters

 WARNING It's only compatible with lua52 (at least only tested with 5.2)

 TODO:

 - Implement commit/rollback
 - Implement disconnect
 - Find how to check for lua-5.2 in configure
 - Add filter_lua.c to configure files
Test if lua function exists before registering them
Merge pull request #433 from bocal/lua_filter

Lua filter