Allow a client to choose if non transacted persistent message should use sync or async send.

ActiveMQ currently sends all messages to the broker using an async send. This allows the client send() method call to be very fast since it does not have to wait for the message to arrive at the server.

Unfortunatly, most folks will assume that the send() method should block when sending a non-transacted persistent message. They will expect the send to work like JDBC operation using auto-commit.

I propose that we add a ConnectionFactory property that controls if non-transacted persistent messages use async sends to the broker.