including behaviour on closed lobjects and stale lobjects.
* psycopg/lobject_type.c (psyco_lobj_close): don't mark the
connection closed here because it is done by
lobject_close_locked().
* psycopg/lobject_int.c (lobject_open): mark objects as not closed
if we successfully open them.
(lobject_close_locked): mark the lobject closed here.
(lobject_export): ensure we are in a transaction, since
lo_export() issues multiple queries.
* psycopg/lobject_type.c (lobject_setup): make lobjects start closed.
