[Distutils] zc.buildout: the extended-by option

[Thomas Lotze]

Jim Fulton wrote:

>> To me, this looks as if it was safe to just remove any traces of the
>> option, including the buggy implementation. The only downside would be
>> that configurations which still use the option would fail silently
>> instead of raising the NameError. I don't consider this to be of much
>> importance in practice, but before going ahead and removing code, I
>> wanted to give people a chance to disagree. Thank you.
> 
> +1
> 
> Perhaps add a check and raise an error if the option is present.

I've just removed the remains of the option's implementation and added a
check that raises a UserError if an extended-by option is still
encountered in some buildout section.

-- 
Thomas