pgsql: Arrange to "inline" SQL functions that appear in a query's FROM

Log Message:
-----------
Arrange to "inline" SQL functions that appear in a query's FROM clause,
are declared to return set, and consist of just a single SELECT. We
can replace the FROM-item with a sub-SELECT and then optimize much as
if we were dealing with a view. Patch from Richard Rowell, cleaned up
by me.

Modified Files:
--------------
pgsql/src/backend/catalog:
pg_proc.c (r1.148 -> r1.149)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/pg_proc.c?r1=1.148&r2=1.149)
pgsql/src/backend/executor:
functions.c (r1.120 -> r1.121)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/functions.c?r1=1.120&r2=1.121)
pgsql/src/backend/optimizer/plan:
planner.c (r1.226 -> r1.227)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planner.c?r1=1.226&r2=1.227)
pgsql/src/backend/optimizer/prep:
prepjointree.c (r1.49 -> r1.50)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepjointree.c?r1=1.49&r2=1.50)
pgsql/src/backend/optimizer/util:
clauses.c (r1.254 -> r1.255)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/clauses.c?r1=1.254&r2=1.255)
pgsql/src/include/executor:
functions.h (r1.30 -> r1.31)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/functions.h?r1=1.30&r2=1.31)
pgsql/src/include/optimizer:
clauses.h (r1.88 -> r1.89)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/clauses.h?r1=1.88&r2=1.89)
prep.h (r1.59 -> r1.60)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/prep.h?r1=1.59&r2=1.60)