Small code cleanup.
Fix missing *pg-dbname* in CSV processing, resulting in broken logging.
Fix monitor logging with no argument is given to the format string.
Take benefits of PostgreSQL COPY error CONTEXT.

This message has the line number where the erroneous data was found on the
server, and given the pre-processing we already done at that point, it's
easy to convert that number into an index into the current batch, an array.

To do do, we need Postmodern to expose the CONTEXT error message and we need
to parse it. The following pull request cares about the Postmodern side of
things:

  https://github.com/marijnh/Postmodern/pull/46

The parsing is done as simply as possible, only assuming that the error
message is using comma separators and having the line number in second
position. The parsing as done here should still work with localized message
strings.

  CONTEXT: COPY errors, line 3, column b: "2006-13-11"

This change should significantly reduce the cost of error processing.