[Cython] Abandon support for Python 2.3?

[Dag Sverre Seljebotn]

> This is a valid point. Also, as we work (via Dag's GSoC project for  
> example) to make it easier to use numpy effectively from Cython, it  
> does seem kind of odd to say "you need 2.3 to use NumPy, but 2.4 to  
> use NumPy+Cython."
I agree, this seems to pretty much override all my arguments.

-- 
Dag Sverre