- Added function literal evaluator (i.e., closure).
- Workaround for d2stacktrace's infinite-loop bug.
   (when std.demangle.demangle use exception inside it,
    it will go into an infinite loop. to avoid this,
    I choose to unset TraceHandler during stacktrace generation.
    This is far from the complete solution, but at least it should
    work as expected under single-thread environment...)