Support attribute index scan with the sql 'IN' operator

[tamas]

OGR currently has only a limited support for attribute index scans. Attribute indexes (mapinfo .IND format) can be created (Currently only for the Shapefile driver) by using an sql command like: [CREATE INDEX ON parcel USING parcel_id]

An index accelerates very simple attribute queries of the form fieldname = value, which is what is used by the JOIN capability. The index cannot be used for fetching multiple values like [select * from parcel where parcel_id=10 or parcel_id=20]

The following patch would add index support to the sql queries by using the 'IN' operator, which would allow to do the equivalent query in the following form: [select * from parcel where parcel_id in (10,20)]

[tamas]

Applied in trunk (r20101)