Add "pausing" of all threads before dumping the stack trace
The following discussion from !653 (merged) should be addressed:
Was talking with Chris Jones about a nifty feature on CMSSW, which I think we should incorporate (though maybe not in this MR?). When an signal is caught and the stack trace printed, ALL threads are immediately paused, so that one gets a meaningful view of the state of the whole system. Otherwise, by the time the stack is captured and printed, the other threads have moved far beyond where they were when the incident happened. This is probably more important for capturing SIGs than exceptions, but it is an incredibly useful feature that we should implement.