Use the Windshaft query-rewriter interface to adapt queries so
they use available overview tables.
This requires a version of Windshaft that implements the query-rewriter
interface (package.json/npm-shrinkwap.json have yet to be updated)
Now data for multiple tables is obtained in one call, simplifying the
use of this function. Also base table is returned as an oid, so we
now have the overview base table names with schema only when needed.
Javier Goizueta