JDBC Connection startup cleaned up

Hi,

I've done some cleaning up in the org.postgresql.Connection class.

This patch

* Introduces a new class, StartupPacket.
* Moves a lot of constants from Connection to StartupPacket.
* Makes two instance variables in Connection into locals.

/Anders
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A n d e r s  B e n g t s s o n                   ndrsbngtssn@yahoo.se
Stockholm, Sweden