- add session.close() w/ rationale to top-level "using transactions"  section.  References #3974
- add session.close() w/ rationale to top-level "using transactions"
 section.  References #3974

Change-Id: Idb650cbe9825cfae893ee917132b5b9d693f0c6c

graingert/sqlalchemy,graingert/sqlalchemy,j5int/sqlalchemy,wujuguang/sqlalchemy,zzzeek/sqlalchemy,monetate/sqlalchemy,monetate/sqlalchemy,wujuguang/sqlalchemy,sqlalchemy/sqlalchemy,j5int/sqlalchemy