BLD/TST: @network, inspect formatted expection rather then str(e)

@jreback, here's the next attempt.
I guess the output we see from pdb and str(e) are not the same thing,
so this compares the strings against a properly formatted exception
(I ommited the traceback, shouldn't be relevent).

I'l rerun this on travis 15 times or so before merging.