pgsql: Extend CTE patch to support recursive UNION (ie, without ALL).

Log Message:
-----------
Extend CTE patch to support recursive UNION (ie, without ALL). The
implementation uses an in-memory hash table, so it will poop out for very
large recursive results ... but the performance characteristics of a
sort-based implementation would be pretty unpleasant too.

Modified Files:
--------------
pgsql/doc/src/sgml:
queries.sgml (r1.46 -> r1.47)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/queries.sgml?r1=1.46&r2=1.47)
pgsql/doc/src/sgml/ref:
select.sgml (r1.105 -> r1.106)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/select.sgml?r1=1.105&r2=1.106)
pgsql/src/backend/executor:
nodeRecursiveunion.c (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeRecursiveunion.c?r1=1.1&r2=1.2)
pgsql/src/backend/nodes:
copyfuncs.c (r1.407 -> r1.408)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.407&r2=1.408)
outfuncs.c (r1.341 -> r1.342)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.341&r2=1.342)
pgsql/src/backend/optimizer/plan:
createplan.c (r1.249 -> r1.250)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c?r1=1.249&r2=1.250)
pgsql/src/backend/optimizer/prep:
prepunion.c (r1.157 -> r1.158)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepunion.c?r1=1.157&r2=1.158)
pgsql/src/backend/parser:
parse_cte.c (r2.2 -> r2.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_cte.c?r1=2.2&r2=2.3)
pgsql/src/include/nodes:
execnodes.h (r1.189 -> r1.190)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h?r1=1.189&r2=1.190)
plannodes.h (r1.104 -> r1.105)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/plannodes.h?r1=1.104&r2=1.105)
pgsql/src/include/optimizer:
planmain.h (r1.113 -> r1.114)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/planmain.h?r1=1.113&r2=1.114)
pgsql/src/test/regress/expected:
with.out (r1.3 -> r1.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/with.out?r1=1.3&r2=1.4)
pgsql/src/test/regress/sql:
with.sql (r1.3 -> r1.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/with.sql?r1=1.3&r2=1.4)