[Csv] Minor change to behaviour of csv module

[Skip Montanaro]

    Andrew> I'm considering a change to the csv module that could
    Andrew> potentially break some obscure uses of the module (but CSV files
    Andrew> usually quote, rather than escape, so the most common uses
    Andrew> aren't effected).

I'm with the other respondents.  This looks like a bug that should be
squashed.

Skip