Spatial filter enhancement of Odbc provider.

[zhanga]

When there is a spatial filter, Fdo Odbc provider just uses the envelope of the filter. It generates a SQL where clause like (X > minX and X < maxX) and (Y > minY and Y <maxY) to filter the features. If we are using complex spatial filter such as circle or triangle, some features that are not in the filter (but in the envelope) will be selected.

We need to add a secondary filter to handle complex spatial filters.