buglist wish 1011: sum(1/(k+a), k=1..n) by Gosper's method

(1) -> sum(1/(k+a), k=1..n)

         n
        --+     1
   (1)  >     -----
        --+   k + a
        k= 1
                                         Type: Union(Expression(Integer),...)

but evaluating by Gosper's method should give

digamm(n+a+1)-digamma(a+1)