Patch for binary transfer of point and box geometric types

Hi,

This patch adds generic support for PGobject subclasses to use binary transfer mode and modifies
PGpoint and PGbox objects to use it.

A PGobject must implement a new PGBinaryObject interface to support binary transfers. I made
it a separate interface so that existing custom PGobject instances need not be modified.

The registration of OIDs is still hard coded in the AbstractJdbc2Connection so no custom types
can yet use the binary transfer feature.

Adding other geometric types is very easy.

-Mikko