Refactor planner's pathkeys data structure to create a separate, explicit

representation of equivalence classes of variables.  This is an extensive
rewrite, but it brings a number of benefits:
* planner no longer fails in the presence of "incomplete" operator families
that don't offer operators for every possible combination of datatypes.
* avoid generating and then discarding redundant equality clauses.
* remove bogus assumption that derived equalities always use operators
named "=".
* mergejoins can work with a variety of sort orders (e.g., descending) now,
instead of tying each mergejoinable operator to exactly one sort order.
* better recognition of redundant sort columns.
* can make use of equalities appearing underneath an outer join.

src/include/optimizer/restrictinfo.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.39 2007/01/05 22:19:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.40 2007/01/20 20:45:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,12 +32,8 @@ extern List *extract_actual_clauses(List *restrictinfo_list,
 extern void extract_actual_join_clauses(List *restrictinfo_list,
 							List **joinquals,
 							List **otherquals);
-extern List *remove_redundant_join_clauses(PlannerInfo *root,
-							  List *restrictinfo_list,
-							  bool isouterjoin);
 extern List *select_nonredundant_join_clauses(PlannerInfo *root,
 								 List *restrictinfo_list,
-								 List *reference_list,
-								 bool isouterjoin);
+								 List *reference_list);
 
 #endif   /* RESTRICTINFO_H */