do not allow duplication of needed_outputs

Author: oesteban

nipype/pipeline/engine/nodes.py

@@ -219,7 +219,7 @@ def needed_outputs(self):
     @needed_outputs.setter
     def needed_outputs(self, new_outputs):
         """Needed outputs changes the hash, refresh if changed"""
-        new_outputs = sorted(new_outputs or [])
+        new_outputs = sorted(list(set(new_outputs or [])))
         if new_outputs != self._needed_outputs:
             # Reset hash
             self._hashvalue = None