stapdyn: Enable end/error probes

stapdyn: Enable end/error probes

The dyninst exit hook runs too late for us to still call anything in the
mutatee, so the systemtap_module_exit() call which should run all of the
end/error probes wasn't happening.

Now we use a destructor function in the mutatee, so our exit path always
runs after main() returns or after an exit() call.  Functions like
_exit() are still problematic though.

This now also makes a distinction between initializing process-local vs.
session resources, so we are more ready for operating with multiple
mutatees at once.  See dyninst/runtime.h for design comments.