The section starting with:
"If a class defines a slot also defined in a base class, the instance
variable
  defined by the base class slot is inaccessible rendering the meaning
of the
  program undefined. [...]"

would need to be revisited as it claims that a check for this issue
might be added in future. As far as I can tell, it has been added in
Python 2.4 or earlier as I get a TypeError in that case.

The attached diff is my attempt to fix this issue.

Kind Regards, 
Sebastian

Additional Information:

"multiple bases have instance lay-out conflict"

This happens only if I add __slots__ to the bases so that there is no
dict. I can reproduce this easily by indirectly deriving a class from
two bases that both define the same slot. 
It only happens if all classes define __slots__ so there is no dict.

class ac( object ):
    __slots__ = "a"

class bc( ac ):
    __slots__ = "b"

class cc( ac ):
    __slots__ = "c"

class cannotbecreated( bc,cc ):
     pass
     # raises an error.

Actually I don't know whether this is intended or if it is related to
the documentation section I pointed at.

As far as I can tell, the text is still correct:

>>> class a(object): __slots__ = 'a'
>>> class b(a): __slots__ = 'a'

works without raising TypeError.

I've nevertheless enhanced the docs a bit in r75610.