python - be: Use get_attro and fill in members structure.

Log Message:
-----------
Use get_attro and fill in members structure.
Change PyHT's tuple descriptor accessor from 'desc' to 'TupleDesc'(like Pg.Type)
Member entries are "virtual" as get_attro will grab them before it would ever
get to GenericGetAttro.
Disallow HT creation if the arg count in tupd_call is not equal to td->natts(no
segfaults? yes please.)

Modified Files:
--------------
be/include/pypg:
heaptuple.h (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/include/pypg/heaptuple.h.diff?r1=1.2&r2=1.3)
postgres.h (r1.3 -> r1.4)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/include/pypg/postgres.h.diff?r1=1.3&r2=1.4)
be/src:
heaptuple.c (r1.3 -> r1.4)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/heaptuple.c.diff?r1=1.3&r2=1.4)
tupledesc.c (r1.4 -> r1.5)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/tupledesc.c.diff?r1=1.4&r2=1.5)