- Calling fetchone() or similar on a result that

- Calling fetchone() or similar on a result that
has already been exhausted, has been closed,
or is not a result-returning result now
raises ResourceClosedError, a subclass of
InvalidRequestError, in all cases, regardless
of backend.  Previously, some DBAPIs would
raise ProgrammingError (i.e. pysqlite), others
would return None leading to downstream breakages
(i.e. MySQL-python).

- Connection, ResultProxy, as well as Session use
ResourceClosedError for all "this
connection/transaction/result is closed" types of
errors.