help with backtrace stuff

I was trying to reintegrate some changes I had made a couple weeks ago 
to make JS backtraces more prevalent. Unfortunately, Adam's patch called 
"fixed heinous breakage, added backtrace support" seems to have broken 
things in a way that I don't understand. The backtrace() method went 
away(fine), and the backtrace Vec never seems to get anything put in 
it(not fine), so it's size is always zero. Can anybody provide some 
insight into what's going on here?

-Tupshin