Clarify COMMIT/ROLLBACK logging when autocommit is turned on
Improved engine logging to note ROLLBACK and COMMIT which is logged while
the DBAPI driver is in AUTOCOMMIT mode. These ROLLBACK/COMMIT are library
level and do not have any effect when AUTOCOMMIT is in effect, however it's
still worthwhile to log as these indicate where SQLAlchemy sees the
"transaction" demarcation.