Northampton's historic district could be expanded by about 22 acres if some residents of the Round Hill neighborhood have their way.  The group is looking to add the Clarke Schools campus to the district, which would add restrictions to how some of its buildings could be developed.  That concerns Clarke Schools President Bill Corwin, who has an agreement with a realty company to sell some of its buildings for redevelopment as apartments.  A decision on expanding the historic district is expected in a few weeks.