add a debug msg function to Lua event
slide_in + text should still be showing text word by word, so don't let slide_in effect call add_complete_rundown()
more hacks to fix: 1. talk_end scripts will skip first sentence, dunno why; 2. fix slide_in can be triggered multiple times when word-by-word is still going; 3. track an old_timer_handle_ to remove LuaJIT ffi callbacks, but currently I am unable to remove the last one.