become an externally usable package but still remains within the main sqlalchemy parent package.
in this system, we use kind of an ugly hack to get the noseplugin imported outside of the
"sqlalchemy" package, while still making it available within sqlalchemy for usage by
third party libraries.
of this object has been simplified and moved into
ExecutionContext. Dialects which support sequences should
add a `fire_sequence()` method to their execution context
implementation. [ticket:1566]
Mike Bayer