Do not write out WCOs in Query

The WithCheckOptions list in Query are only populated during rewrite and
do not need to be written out or read in as part of a Query structure.

Further, move WithCheckOptions to the bottom and add comments to clarify
that it is only populated during rewrite.

Back-patch to 9.5 with a catversion bump, as we are still in alpha.

src/include/nodes/parsenodes.h

@@ -130,8 +130,6 @@ typedef struct Query
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
-	List	   *withCheckOptions;		/* a list of WithCheckOption's */
-
 	OnConflictExpr *onConflict; /* ON CONFLICT DO [NOTHING | UPDATE] */
 
 	List	   *returningList;	/* return-values list (of TargetEntry) */
@@ -158,6 +156,10 @@ typedef struct Query
 
 	List	   *constraintDeps; /* a list of pg_constraint OIDs that the query
 								 * depends on to be semantically valid */
+
+	List	   *withCheckOptions;	/* a list of WithCheckOption's, which are
+									 * only added during rewrite and therefore
+									 * are not written out as part of Query. */
 } Query;