[Cython] moving the iter-range optimisation into a transform

[Stefan Behnel]

Hi,

initially, the iter-range transform was done during the analysis phase
inside the For*StatNode, which feels a bit misplaced now that we have
nicely working tree transformations. I tried moving it out into a transform
(actually next to the iter-dict transform), but it's currently a "works for
me". I'm pretty sure there are cases I forgot where this doesn't work
(yet). It's definitely worth a review, and it would be nice if a few people
could give it a try with their code base and check if the generated code
comes out as expected.

http://hg.cython.org/cython-devel/rev/c1a7180ac974

Thanks!

Stefan