They now take ownership of the src argument.
Needed to change Scan to make a copy of []byte arguments as lib/pq apparently
gives Scan a shared memory buffer.
Because reading a record type requires the decoder to be able to look up oid
to type mapping and types such as hstore have types that are not fixed between
different PostgreSQL servers it was necessary to restructure the pgtype system
so all encoders and decodes take a *ConnInfo that includes oid/name/type
information.
