Adjust ExplainOneQuery_hook_type to take a DestReceiver argument.

The materialized views patch adjusted ExplainOneQuery to take an
additional DestReceiver argument, but failed to add a matching
argument to the definition of ExplainOneQuery_hook.  This is a
problem for users of the hook that want to call ExplainOnePlan.
Fix by adding the missing argument.

src/include/commands/explain.h

@@ -47,6 +47,7 @@ typedef void (*ExplainOneQuery_hook_type) (Query *query,
 													   IntoClause *into,
 													   ExplainState *es,
 													 const char *queryString,
+													   DestReceiver *dest,
 													   ParamListInfo params);
 extern PGDLLIMPORT ExplainOneQuery_hook_type ExplainOneQuery_hook;