Replacement for @raoulb pr#914

See #914

ToDo:
- [x] tests
- [x] final rebase
On Fri, Jul 18, 2014 at 05:35:06PM -0700, raoulb wrote:
>    In sympy/functions/elementary/trigonometric.py:
>  > +    def fdiff(self, argindex=1):
>  > +        return self._calculate_reciprocal("fdiff", argindex)
> 
>    Huh?

?