pgsql: Make SubPlan nodes carry the result's typmod as well as datatype

Log Message:
-----------
Make SubPlan nodes carry the result's typmod as well as datatype OID. This is
for consistency with the (relatively) recent addition of typmod to SubLink.
An example of why it's a good idea is to be seen in the recent "failed to
locate grouping columns" bug, which wouldn't have happened if a SubPlan
exposed the same typmod info as the SubLink it was derived from.

This could be back-patched, since it doesn't affect any on-disk data format,
but for the moment it doesn't seem necessary to do so.

Modified Files:
--------------
pgsql/src/backend/nodes:
copyfuncs.c (r1.425 -> r1.426)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.425&r2=1.426)
equalfuncs.c (r1.349 -> r1.350)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.349&r2=1.350)
nodeFuncs.c (r1.38 -> r1.39)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/nodeFuncs.c?r1=1.38&r2=1.39)
outfuncs.c (r1.353 -> r1.354)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.353&r2=1.354)
pgsql/src/backend/optimizer/plan:
subselect.c (r1.146 -> r1.147)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/subselect.c?r1=1.146&r2=1.147)
pgsql/src/include/nodes:
primnodes.h (r1.146 -> r1.147)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/primnodes.h?r1=1.146&r2=1.147)