pg_overexplain: Call previous hooks as appropriate.

It makes no sense to remember the previous values of the hook variables
and then never bother calling those functions. Thanks to Andrei for
spotting my goof.

Author: Andrei Lepikhov <lepihov@gmail.com>
Discussion: http://postgr.es/m/41a344e3-ffb1-4296-8ba7-801f1e9642e5@gmail.com

contrib/pg_overexplain/pg_overexplain.c

@@ -135,6 +135,10 @@ overexplain_per_node_hook(PlanState *planstate, List *ancestors,
 	overexplain_options *options;
 	Plan	   *plan = planstate->plan;
 
+	if (prev_explain_per_node_hook)
+		(*prev_explain_per_node_hook) (planstate, ancestors, relationship,
+									   plan_name, es);
+
 	options = GetExplainExtensionState(es, es_extension_id);
 	if (options == NULL)
 		return;
@@ -251,6 +255,10 @@ overexplain_per_plan_hook(PlannedStmt *plannedstmt,
 {
 	overexplain_options *options;
 
+	if (prev_explain_per_plan_hook)
+		(*prev_explain_per_plan_hook) (plannedstmt, into, es, queryString,
+									   params, queryEnv);
+
 	options = GetExplainExtensionState(es, es_extension_id);
 	if (options == NULL)
 		return;