src/csv.c: use a bigger buffer

src/csv.c: use a bigger buffer

The CSV plugin formerly used a relatively small output buffer. If you
had a large dataset, you would always get error -1 because the line
length was be too long. This patch extends the buffer.

Signed-off-by: Colin McCabe <colin.mccabe@dreamhost.com>
Signed-off-by: Florian Forster <octo@huhu.verplant.org>