Removed the unused import of the __builtin__ module by the prompt.tab_completion module.
See the thread starting at https://mail.gna.org/public/relax-devel/2007-02/msg00003.html
(Message-id: <45DACFEA.7020108@...>) for a discussion of the issue.
The text "__builtins__" has been fixed and is now "__builtin__".
