Add more logging to benchmarking.CSVComparison

[fredshone]

The CSV comparison class (here) has no logging (other than what it receives from it's parent class.

This led to a difficult to resolve bug where input benchmark data had the wrong column names.

Suggest:

i) add better logging (not necessarily more, unless in debug)
ii) consider not crashing when broken bm data is found - NOT SURE ABOUT THIS THOUGH