dbgtrace, does a trace if --debug was used
csv and general reader fixes, cleanups

- The CSV reader no longer writes a "(stdin).rules" file when reading
  from stdin.

- Selection of reader(s) is now smarter when input is coming from stdin.
  Previously, all readers were considered applicable for stdin.  This
  meant that when reading a CSV file from stdin, the journal and timelog
  readers were always tried first, and if the CSV file was unparseable,
  you'd see the first (journal) reader's error instead of the CSV
  reader's.  Now, the readers do some basic content sniffing when
  reading stdin, so it generally tries only the one right reader and
  we'll see the right errors.

- The read system now has more debug output.