pgsql-server: Make the world very nearly safe for composite-type columns

Log Message:
-----------
Make the world very nearly safe for composite-type columns in tables.
1. Solve the problem of not having TOAST references hiding inside composite
values by establishing the rule that toasting only goes one level deep:
a tuple can contain toasted fields, but a composite-type datum that is
to be inserted into a tuple cannot. Enforcing this in heap_formtuple
is relatively cheap and it avoids a large increase in the cost of running
the tuptoaster during final storage of a row.
2. Fix some interesting problems in expansion of inherited queries that
reference whole-row variables. We never really did this correctly before,
but it's now relatively painless to solve by expanding the parent's
whole-row Var into a RowExpr() selecting the proper columns from the
child.
If you dike out the preventive check in CheckAttributeType(),
composite-type columns now seem to actually work. However, we surely
cannot ship them like this --- without I/O for composite types, you
can't get pg_dump to dump tables containing them. So a little more
work still to do.

Modified Files:
--------------
pgsql-server/src/backend/access/common:
heaptuple.c (r1.91 -> r1.92)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/common/heaptuple.c.diff?r1=1.91&r2=1.92)
pgsql-server/src/backend/access/heap:
tuptoaster.c (r1.42 -> r1.43)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/heap/tuptoaster.c.diff?r1=1.42&r2=1.43)
pgsql-server/src/backend/optimizer/path:
allpaths.c (r1.117 -> r1.118)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/path/allpaths.c.diff?r1=1.117&r2=1.118)
costsize.c (r1.129 -> r1.130)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/path/costsize.c.diff?r1=1.129&r2=1.130)
pathkeys.c (r1.59 -> r1.60)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/path/pathkeys.c.diff?r1=1.59&r2=1.60)
pgsql-server/src/backend/optimizer/prep:
prepunion.c (r1.112 -> r1.113)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/prep/prepunion.c.diff?r1=1.112&r2=1.113)
pgsql-server/src/backend/optimizer/util:
relnode.c (r1.59 -> r1.60)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/util/relnode.c.diff?r1=1.59&r2=1.60)
tlist.c (r1.64 -> r1.65)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/util/tlist.c.diff?r1=1.64&r2=1.65)
pgsql-server/src/backend/utils/cache:
typcache.c (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/cache/typcache.c.diff?r1=1.6&r2=1.7)
pgsql-server/src/include/access:
tuptoaster.h (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/access/tuptoaster.h.diff?r1=1.17&r2=1.18)
pgsql-server/src/include/nodes:
relation.h (r1.95 -> r1.96)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/nodes/relation.h.diff?r1=1.95&r2=1.96)
pgsql-server/src/include/utils:
typcache.h (r1.3 -> r1.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/utils/typcache.h.diff?r1=1.3&r2=1.4)