pgsql: Replace the usage of heap_addheader to create pg_attribute tuples

Log Message:
-----------
Replace the usage of heap_addheader to create pg_attribute tuples with regular
heap_form_tuple. Since this removes the last remaining caller of
heap_addheader, remove it.

Extracted from the column privileges patch from Stephen Frost, with further
code cleanups by me.

Modified Files:
--------------
pgsql/src/backend/access/common:
heaptuple.c (r1.123 -> r1.124)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/heaptuple.c?r1=1.123&r2=1.124)
pgsql/src/backend/catalog:
heap.c (r1.343 -> r1.344)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/heap.c?r1=1.343&r2=1.344)
index.c (r1.308 -> r1.309)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/index.c?r1=1.308&r2=1.309)
pgsql/src/backend/commands:
tablecmds.c (r1.269 -> r1.270)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablecmds.c?r1=1.269&r2=1.270)
pgsql/src/include/access:
htup.h (r1.103 -> r1.104)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/htup.h?r1=1.103&r2=1.104)
pgsql/src/include/catalog:
heap.h (r1.88 -> r1.89)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/heap.h?r1=1.88&r2=1.89)