[Cython] Proposed change to behaviour of "not None"

Lisandro Dalcin wrote:

> I know, I can (and I do) use 'Type arg is not
> None' in argument lists, but I never liked it.

Speaking of that, I've been thinking for a while now
about making "not None" the default, and requiring
"or None" to specify that None is an acceptable
parameter value.

Having seen a number of pieces of Pyrex code that
were susceptible to being crashed because "not None"
wasn't used where it should have been, I think
this would be a safer default. The change may
break some existing code, though.

What do people think?

-- 
Greg