Now that we have an ORTE thread running in apps, we can't just call "exit"
during RTE abort as that is happening in a thread, and (at least in some
environments) doesn't result in the main thread being immediately
terminated. Instead, we wind up going thru orte_finalize in the main
thread, which isn't what we want.

So replace the call to "exit" with the "quick exit" variant "_exit", which
causes the entire process to exit immediately.

(custom patch has been posted for 1.8.3)