Replacement for @raoulb pr#914

See #914

ToDo:
- [x] tests
- [x] final rebase
On Fri, Jul 18, 2014 at 05:30:38PM -0700, raoulb wrote:
>    In sympy/functions/elementary/trigonometric.py:
> 
>  >
>  > -    Examples
>  > +    def _calculate_reciprocal(self, method_name, *args, **kwargs):
>  > +        # If calling method_name on _reciprocal_of returns a value != None
>  > +        # then return the reciprocal of that value
> 
>    Maybe better make docstrings?

This is a private method.  I think, this is fine.