stats.py should fail helpfully when results.csv is broken

[dfarrell07]

Currently, there's no error handling code in stats.py to deal with malformed results.csv files. Anything other than the expected result of WCBench runs breaks with obtuse stack traces. Should catch that Exception and fail with some helpful debugging info.

Should be fairly easy for anyone who knows some Python, so marking as "good for beginners".

This came out of a question in #62.