If a problem does exit(10), should give a better message than "RTE"

[rokicki]

Right now if a submission does exit(10), verifyproblem treats this as an RTE, despite the fact that there is no runtime exception. To save the judges a lot of time tracking down an issue in a submission that doesn't really exist, verifyproblem should report "non-zero exit code; treating as RTE" or some such.