Update NEWS.txt

NEWS.txt

@@ -28,6 +28,10 @@ New Features
    anything below an intermediate variable that has a name. Defaults to False.
  * debugprint does not print anymore the "|" symbol in a column after the last input.
 
+Internal changes
+ * Define new exceptions MissingInputError and UnusedInputError, and use them
+   in theano.function, instead of TypeError and ValueError. (Pascal L.)
+
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 Release Notes
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