Add schema support to PG driver in ogr2ogr

[sfrost@…]

Schemas in PostgreSQL are seperate namespaces with permissions per
namespace (create or usage) and there's a 'search_path' variable that
lists out the schemas to be searched for when no specific schema is
given.  It's alot like Oracle accounts except you don't actually have to
have an account to have a schema, which is *very* nice.  Generally each
*real* user has his/her own schema though, except for role accounts
which just use other schemas.  Schemas are tracked in Postgres via the
pg_namespace system table.

Example:
Login as user sfrost; default search_path is '$user,public'.
Now, there exists a 'sfrost' schema, so that's what I'm looking at when
I first log in and do \d.  I *only* see things in the 'sfrost' schema
and the 'public' schema though.  Now, say there's another schema called
'lerg', I can reference that schema directly by saying:

select * from lerg.table;

Assuming I have 'usage' rights on the schema 'lerg' and select rights on
the table 'lerg.table'.

Now, what happened when I ran ogr2ogr was that it dumped the new tables
into 'sfrost', my default schema.  What I'd like to have happen is for
the tables to be loaded into their own schema.  I wouldn't expect
ogr2ogr to actually create the schema, that's generally an operation
reserved for the database superuser.  What I'd like is the ability to
tell ogr2ogr what schema to use.  Having support directly in
ogr2ogr would mean that you could then specify a list of *schemas* to
search for layers, instead of tables, which would make things easier
both from an ogr2ogr point of view and from a user's point of view, I'd
think.  Additionally, it doesn't appear possible to specify a schema to use in
the PGconnectdb string.

From what I can tell ogr2ogr just needs to issue a 'set schema_path to %s'
command where the %s is provided on the command-line to get basic schema support.