Fix contrib/postgres_fdw to handle multiple join conditions properly.

The previous coding supposed that it could consider just a single join
condition in any one parameterized path for the foreign table.  But in
reality, the parameterized-path machinery forces all join clauses that are
"movable to" the foreign table to be evaluated at that node; including
clauses that we might not consider safe to send across.  Such cases would
result in an Assert failure in an assert-enabled build, and otherwise in
sending an unsafe clause to the foreign server, which might result in
errors or silently-wrong answers.  A lesser problem was that the
cost/rowcount estimates generated for the parameterized path failed to
account for any additional join quals that get assigned to the scan.

To fix, rewrite postgresGetForeignPaths so that it correctly collects all
the movable quals for any one outer relation when generating parameterized
paths; we'll now generate just one path per outer relation not one per join
qual.  Also fix bogus assumptions in postgresGetForeignPlan and
estimate_path_cost_size that only safe-to-send join quals will be
presented.

Based on complaint from Etsuro Fujita that the path costs were being
miscalculated, though this is significantly different from his proposed
patch.

Author: tglsfdc

contrib/postgres_fdw/deparse.c

@@ -134,14 +134,15 @@ static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
 
 
 /*
- * Examine each restriction clause in baserel's baserestrictinfo list,
- * and classify them into two groups, which are returned as two lists:
+ * Examine each qual clause in input_conds, and classify them into two groups,
+ * which are returned as two lists:
  *	- remote_conds contains expressions that can be evaluated remotely
  *	- local_conds contains expressions that can't be evaluated remotely
  */
 void
 classifyConditions(PlannerInfo *root,
 				   RelOptInfo *baserel,
+				   List *input_conds,
 				   List **remote_conds,
 				   List **local_conds)
 {
@@ -150,7 +151,7 @@ classifyConditions(PlannerInfo *root,
 	*remote_conds = NIL;
 	*local_conds = NIL;
 
-	foreach(lc, baserel->baserestrictinfo)
+	foreach(lc, input_conds)
 	{
 		RestrictInfo *ri = (RestrictInfo *) lfirst(lc);