bugfix: dlgIndex column order

Hi, all

Bug fix:
only when index's type is btree, user can set column order.
reported by: Obe, Regina

> I see that the new version of PgAdmin now automatically puts in for
> CREATE INDEX a
>
> the new NULLS FIRST / LAST clause for PostgreSQL 8.4.
>
> Unfortunately when you try to use this for a gist index -- it generates
> something like this
>
> CREATE INDEX mytable_idx_the_geom
> ON mytable USING gist (poi_geom ASC NULLS LAST);
>
> Which generates an error from PostgreSQL like this.
>
> access method "gist" does not support ASC/DESC options
>
> There doesn't seem to be a way to turn this off except by explicitly
> editing the SQL statement to remove the ASC clause. Can we have it not
> enabled by default or if we must -- allow this to be unchecked.
>
> Thanks,
> Regina

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Quan Zongliang
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