SEARCH and CYCLE clauses

This adds the SQL standard feature that adds the SEARCH and CYCLE
clauses to recursive queries to be able to do produce breadth- or
depth-first search orders and detect cycles.  These clauses can be
rewritten into queries using existing syntax, and that is what this
patch does in the rewriter.

Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com

src/include/parser/parse_node.h

@@ -78,6 +78,7 @@ typedef enum ParseExprKind
 	EXPR_KIND_CALL_ARGUMENT,	/* procedure argument in CALL */
 	EXPR_KIND_COPY_WHERE,		/* WHERE condition in COPY FROM */
 	EXPR_KIND_GENERATED_COLUMN, /* generation expression for a column */
+	EXPR_KIND_CYCLE_MARK,		/* cycle mark value */
 } ParseExprKind;
 
 
@@ -294,6 +295,7 @@ struct ParseNamespaceColumn
 	Oid			p_varcollid;	/* OID of collation, or InvalidOid */
 	Index		p_varnosyn;		/* rangetable index of syntactic referent */
 	AttrNumber	p_varattnosyn;	/* attribute number of syntactic referent */
+	bool		p_dontexpand;	/* not included in star expansion */
 };
 
 /* Support for parser_errposition_callback function */