[Cython] Temp allocation flow

[Greg Ewing]

Dag Sverre Seljebotn wrote:
> It 
> now takes two parameters, "decref" and "free_temp", which both defaults 
> to True, and which can be toggled.

Rather than a free_temp parameter, I'd be more inclined
to have an owns_temp flag on the node, set according to
whether the node allocated the temp itself or it was
supplied by the parent (currently done via an optional
parameter to allocate_temps(), which would become a
parameter to generate_evaluation_code()).

-- 
Greg