wip
Use database/sql style transaction interface
Failing to write to Conn.conn kills Conn
Remove commented out test
Reorganize code
Add timestamp support

But not to NullTime because of text vs binary encoding difficulties.

You really should never use timestamp anyway.
EncodeBinary checks oid of param
NullX Scan check oids
Rows does not expose MsgReader
Change Scan / decodeX to use ValueReader

Also improve Rows.Scan and Rows.Values error handling.