Fix issue with missing column types in explain

presto-main/src/main/java/com/facebook/presto/sql/planner/PlanPrinter.java

@@ -452,7 +452,7 @@ private Void processExchange(ExchangeNode node, int indent)
         {
             for (PlanFragmentId planFragmentId : node.getSourceFragmentIds()) {
                 PlanFragment target = fragmentsById.get().get(planFragmentId);
-                target.getRoot().accept(this, indent);
+                target.getRoot().accept(new Visitor(target.getSymbols(), fragmentsById), indent);
             }
             return null;
         }