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

Issue 477: PgServer binary transmission of query params is unimplemented, patch from Andrew Franklin

Improve error message when we have a unique constraint violation, displays the offending key in the error message