Add comments to export logic

Add comments to export logic.
Add a few more comments

Add a few more comments.
Add data connection specific concatenate operators

Add specific concatenate operators to each data connection type so that
fields can be concatenated in sql statements.
Create a new class for the export fields

Create a new class for the export fields.
Add new settings for some lookup table columns

Add new settings for some lookup table columns.
Update the export_fields table dataset definition

Update the dataset definition for the export_fields table.
Add ArcGIS specific concatenate operator

Add ArcGIS specific concatenate operator.
Add MapInfo specific concatenate operator

Add MapInfo specific concatenate operator.
Add static values for some lookup table columns

Add static values for some lookup table columns.
Initial updates to re-order export file columns

Initial updates to re-order export file columns by interweaving
consecutive fields from the same table.
Fix bug with duplicated source outputs

Fix bug with duplicated source outputs and allow multiple output field
names to be numbered within the field name.
Rename confusingly named checkbox

Rename confusingly named checkbox.
Remove export descriptions checkbox from interface

Remove export descriptions checkbox from the export user interface as
this option is now field specific via the export_fields table.
Tweak export interface layout

Tweak export interface layout.
Set Odbc concatenate operators

Set Odbc concatenate operators.
Output dates in required format

Output dates in required format.
Various MapInfo improvements

Various MapInfo improvements.
Add a new setting for max MapInfo record length

Add a new setting for the maximum MapInfo record length allowable in a
table.
Ignore case during export to avoid duplicate fields

Ignore case during export to avoid duplicate fields.
Let user add exported features to MapInfo (CR16)

Let user add exported features to MapInfo (CR16).