The old contract library tried to be glog-friendly in its failfast behavior.
It turns out glog seldom does the right thing when goroutines are involved
(which, as of last sprint, they now are). We already had issues with stacks
not getting printed when --logtostderr was turned on, and the code tried
to work around this; but this still didn't work for the goroutines case.
All of this seems like way too much cleverness. Let's just use Go panics.
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