add a crash handler at initialization

I'm just addressing the comments you made here: that the exception handler is for the main thread, not the child threads. If you *are* trying to address child threads, I'd just like to be clear about what the goals are. Also, this is the first I'm hearing in this discussion about GHCi or yesod devel. So I think it's worth starting over with a simple question:

What exactly is your goal in writing this exception handler?