move the DatabaseEventLister into inner classes - makes it easier to see what belongs to what, especially when some of the the overriden methods are very similar to methods in the superclass (TestBase)

change the PageStore#changeCount field from an int to a long, to cope with databases with very high transaction rates.

somebody reported an error, and they think the PageStore#changeCount field has wrapped and become negative.
Put a check in place to make such a situation more obvious.

Issue 481: Further extensions to PgServer to support better support PG JDBC, patch from Andrew Franklin.

 - methods can be private
 - return value from method unused
 - don't throw an exception which would drop the ODBC connection, rather just send an error response