Provide a way to not add "built-in function" or "in module ..." to every function

These clutter genindex page with no value when there is only one module.

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- Bitbucket: https://bitbucket.org/birkenfeld/sphinx/issue/1295
- Originally reported by: Alexander Schepanovski
- Originally created at: 2013-10-20T13:18:38.171
