#804 at least warning about mismatch between exchange and post_excha…

[petersilva]

• closes in a poll, post_exchange and exchange should match... should we complain if they don't. #804

Add a message:

           if px != self.o.exchange:
                logger.warning( f"post_exchange: {px} is different from exchange: {self.o.exchange}. The settings need for multiple instances to share a poll." )
            else:
                logger.info( f"Good! post_exchange: {px} and exchange: {self.o.exchange} match so multiple instances to share a poll." )

either an info priority message congratulating for matching settings, or a warning bleat if they don't. Give the analyst a clue that something is wrong.