alternating the builtin functions

[Jeff Epler]

$ python
>>> print __builtins__
<module '__builtin__' (built-in)>

$ python -c 'print __builtins__'

$ echo 'print __builtins__ ' > m.py
$ python -c 'import m'
[contents of a dictionary]

For some reason, __builtins__ has long been a different thing in
__main__ than in any other module.  To get consistent behavior, use
'import __builtin__' (that's always a module).

I think that the behavior/definition/value of __builtins__ is considered
an implementation detail.  The closest I found to an admission of this
fact was here:
	http://python.org/doc/ref/exec.html#l2h-563

Jeff