let the postprocessors use the mapnik::map object intellegently

so we needed some more information about the tile we were working with in the postprocessor (well at least to be able to do merging it was handy). so i've added sending the mapnik::map object along to the processing function of the izers. this fixes a bug in the zoom level config stuff that decides based on the config which izer to run on which requests. it was always passing in 0 for every request which means only the izers configured to run on zl 0 would have been run on any requests.
Pretty clear we need a test for this at this point!
Am 29.10.2014 18:08 schrieb "Matt Amos" <notifications@github.com>:

> In src/post_processor.cpp:
>
> >      for (auto range_child : layer_child.second) {
> > -      zoom_range_t zoom_range;
> > -      zoom_range.minzoom = range_child.second.get<int>("minzoom");
> > -      zoom_range.maxzoom = range_child.second.get<int>("maxzoom");
> > +      scale_range_t scale_range;
> > +      scale_range.minscale = zoom_to_scale(range_child.second.get<int>("minzoom"));
>
> Since scale and zoom are inversely related, shouldn't minscale =
> zoom_to_scale(maxzoom)? And similar for maxscale?
>
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> <https://github.com/MapQuest/avecado/pull/30/files#r19575958>.
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