don't throw an error when a select clause outputs multiple copies of …

…the same attribute.

src/main/scala/catalyst/plans/logical/LogicalPlan.scala

@@ -41,7 +41,7 @@ abstract class LogicalPlan extends QueryPlan[LogicalPlan] {
       option.name == remainingParts.head
     }
 
-    options match {
+    options.distinct match {
       case a :: Nil => Some(a) // One match, use it.
       case Nil => None         // No matches.
       case ambiguousReferences =>