Patch from strk:

Patch from strk:
- "\t" always preceeded the first value of a dump_format query
  if NULL

- field values where quoted with (") in dump_format when
  called with -k ( did I introduce that? )

- Appropriate calls to DBF[..]ReadAttributes based on
  cached attribute types.

- Assured that *all* shapes are NULL before exiting with
  an error ( I did not check that NULL shapes in the midle
  of the shapefiles are handled, but previous code did
  not check that either ... )

git-svn-id: http://svn.osgeo.org/postgis/trunk@305 b70326c6-7e19-0410-871a-916f4a2858ee