Add obsolete native testing under ref/test-native

This codes comes from 'test_native' makefile target. It is now obsolete
and it is not used. Just keeping in place to get quick reference points
and checking results against current and faster code.

* ref/test-native/README.txt
* ref/test-native/pf_test_native.c
* ref/test-native/pf_test_native.lua