introduce "autobegin" concept for Connection

introduce "autobegin" concept for Connection

because engine.connect() and engine.begin() should feature
identical internal behavior, with the sole exception that
one rolls back and the end and the other commits at the end,
while also supporting execution options like transaction isolation level
at the connection level, include that engine.connect() will
return a connection that uses autobegin in the same way as the
session will.   This is solely to support the "begin" event
noting that a transaction is begun which is tracked on the
connection.    Behavior and design should be very similar to that
of the ORM session and "Transaction" should no longer be a very
explicit object.

Change-Id: I9c317d242ca7a435de0f17b1618355e29a10d1bc