Postgres: fix dialect to work in databases with mutiple schema and search_path set

In postgres you can have a database with multiple schemas, and configure a particular account to use only a particular schema (by setting something called search_path).

When I use hbm2dll to auto-create my schema objects, sequences are not created if they exist in another schema somewhere in the database, because the dialect simply queries the pg_class catalog for any sequences by that name, even if they are not in the current search path.

Modifying PostgreSQLDialect to use the following query seems to this issue for us. Suggest consideration for inclusion in the postgres dialect. Have not evaluated pg version compatibility.

using hibernate 3.3.1, but verified version on trunk has this same issue.

@Override
public String getQuerySequencesString() {
// return "select relname from pg_class where relkind='S'";

// only return sequences which are visible in the current search path
return "SELECT relname FROM pg_class WHERE relkind='S' and pg_table_is_visible(oid)";
}