Fix some minor issues exposed by outfuncs/readfuncs testing.

Fix some minor issues exposed by outfuncs/readfuncs testing.

A test patch to pass parse and plan trees through outfuncs + readfuncs
exposed several issues that need to be fixed to get clean matches:

Query.withCheckOptions failed to get copied; it's intentionally ignored
by outfuncs/readfuncs on the grounds that it'd always be NIL anyway in
stored rules.  This seems less than future-proof, and it's not even
saving very much, so just undo the decision and treat the field like
all others.

Several places that convert a view RTE into a subquery RTE, or similar
manipulations, failed to clear out fields that were specific to the
original RTE type and should be zero in a subquery RTE.  Since readfuncs.c
will leave such fields as zero, equalfuncs.c thinks the nodes are different
leading to a reported mismatch.  It seems like a good idea to clear out the
no-longer-needed fields, even though in principle nothing should look at
them; the node ought to be indistinguishable from how it would look if
we'd built a new node instead of scribbling on the old one.

BuildOnConflictExcludedTargetlist randomly set the resname of some
TargetEntries to "" not NULL.  outfuncs/readfuncs don't distinguish those
cases, and so the string will read back in as NULL ... but equalfuncs.c
does distinguish.  Perhaps we ought to try to make things more consistent
in this area --- but it's just useless extra code space for
BuildOnConflictExcludedTargetlist to not use NULL here, so I fixed it for
now by making it do that.

catversion bumped because the change in handling of Query.withCheckOptions
affects stored rules.

Discussion: https://postgr.es/m/17114.1537138992@sss.pgh.pa.us