Teach planner about some cases where a restriction clause can be

propagated inside an outer join.  In particular, given
LEFT JOIN ON (A = B) WHERE A = constant, we cannot conclude that
B = constant at the top level (B might be null instead), but we
can nonetheless put a restriction B = constant into the quals for
B's relation, since no inner-side rows not meeting that condition
can contribute to the final result.  Similarly, given
FULL JOIN USING (J) WHERE J = constant, we can't directly conclude
that either input J variable = constant, but it's OK to push such
quals into each input rel.  Per recent gripe from Kim Bisgaard.
Along the way, remove 'valid_everywhere' flag from RestrictInfo,
as on closer analysis it was not being used for anything, and was
defined backwards anyway.

src/include/optimizer/restrictinfo.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.31 2005/06/09 04:19:00 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.32 2005/07/02 23:00:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,11 +19,9 @@
 
 extern RestrictInfo *make_restrictinfo(Expr *clause,
 									   bool is_pushed_down,
-									   bool valid_everywhere,
 									   Relids required_relids);
 extern List *make_restrictinfo_from_bitmapqual(Path *bitmapqual,
-											   bool is_pushed_down,
-											   bool valid_everywhere);
+											   bool is_pushed_down);
 extern bool restriction_is_or_clause(RestrictInfo *restrictinfo);
 extern List *get_actual_clauses(List *restrictinfo_list);
 extern void get_actual_join_clauses(List *restrictinfo_list,