[Pyrex] Pyrex checks type of literal None argument

[Greg Ewing]

Stefan Behnel wrote:

>   value = factory(somepointer, None)
> 
> Pyrex generates this code for it:
> 
>   if (!__Pyx_TypeTest(Py_None, __pyx_ptype_5etree__SomeType)) { ... }

At the point where this is done, Pyrex doesn't know
that it's not just a generic Python value.

I could perhaps be a bit smarter about handling the
types of constant expressions. I'll file this under
Suggestions.

Thanks,
Greg