$B%A%1%C%H(B #3917 $B$,99?7$5$l$^$7$?!#(B (by Yui NARUSE)
$B%9%F!<%?%9(B Open$B$+$i(BAssigned$B$KJQ99(B
$BC4Ev<T(B Koichi Sasada$B$K%;%C%H(B
ko1 changes implementation around iseq and may change the order of
vm_backtrace_each,
so he want us to wait for completion those changes.