TAdvDBFilter enhancements

Add the ability to reference field_names in the "Value" edit box.

That way things like "find all orders that shipped late" would be possible:

order_require_date < order_shipped_date

Either add a new check box (beside the "Case" check box) to indicate "treat value as field name", or parse out some "field markers" - eg:
order_require_date < [[order_shipped_date]]

Actually, if you parsed out the markers as parentheses, it would be possible to add calcs:

safety_stock < [[ on_hand_qty - on_order_qty ]]

Which would resolve to
(safety_stock < (on_hand_qty - on_order_qty) )

The end user would have to manually key in the field names, but even so - I think it would be quite useful to be able to treat the Value entry as an Expression...