New postgres provider

[Vivien Malerba <malerba linuxbox com>]

Hi Rodrigo!

I've just commited a new revision of the Postgres provider which implement the
schemas as follows:

SCHEMA_TABLES:
returns (name, comments)
* OBJECT_NAME may be given to specify one table in particular
* EXTRA_INFO: if specified returns (name, owner, comments, SQL definition)

PROV_TYPES:
returns (name, comments)
* OBJECT_NAME may be given to specify the SQL data type
* EXTRA_INFO: if specified returns (name, comments, owner, GDA type
(GDA_TypeVarchar as default), SQL type)  <--- changed since last time!

For this I've implemented a kind of replacement method which replaces the
contents given by PGresult to fit the needs of the GDA layer. This is done
in the gda-postgres-recset.c::fill_field_values(). So some data (like the SQL
definition of the table) is computed each time the user changed the cursor in
the recordset. Tell me if you think this is a good idea (for speed
reasons) before I continue to implement it for other schemas.

And could you (since I'm not at ease with all this CORBA stuff) modify the
schemas to allow one to query sequences and the parents of a tables. Thanks.

Cheers
Vivien