verified backport of pow grad

theano/scalar/basic.py

@@ -775,8 +775,6 @@ class Pow(BinaryScalarOp):
 
         return (first_part, second_part)
 
-        #return (gz * y * x**(y - 1) if x.type in grad_types else None,
-        #        gz * log(x) * x**y if y.type in grad_types else None)
 pow = Pow(upcast_out, name = 'pow')
 
 class Clip(ScalarOp):