That's the old way of exporting to lua. Starting with 5.0, there is a common interface named kemi that allows exporting same function at once to all kemi-enabled embedded interpreter (at this moment being app_lua, app_jsdt and app_python).
mt_match() is exported to kemi and should be accessible via KSR.mtree.mt_match(str, str, int)
The exports via kemi are not yet properly documented, but you can list them via RPC interface -- if you load app_lua module, see:
- http://kamailio.org/docs/modules/devel/modules/app_lua.html#app_lua.r.list