Add Makefile logic to ease compilation against luajit

Taken from lextlib and lua-term
Bump lua-term for easier compilation against luajit
Fix PAM_PROMPT_ECHO_OFF conversation calling old cutil module instead of new term
Remove pam_util (unnecessary since lua-term), update example to new constants, update its conversation function from pwauth_pam.lua, make it query the username instead of hardcoding "test"