[Cython] FlattenInListTransform again

[Stefan Behnel]

Dag Sverre Seljebotn wrote:
> Just a note that I've disabled FlattenInListTransform as that removed some
> leaks, making the assumption that speed regression is better than leaks.
> Just enable it in Main.py if you disagree/want to pursue it.
> 
> http://trac.cython.org/cython_trac/ticket/199

I've already fixed it, will commit it when I see the test suite pass nicely.

Stefan