make tolerance_iterator exponential
update agg reference images
update cairo reference images
update grid reference images
close sqlite db after testing
get sqlite rtree tests passing on windows - refs #1871 and #2530
remove unneeded boost/cast.hpp header
remove uneeded include
fix geojson plugin linking #2535
fix mapnik/node-mapnik#332
Merge pull request #2514 from mapycz/perf-tolerance-iterator

exponential tolerance_iterator
update a few visual tests based on osx+mapnik-packaging deps
always return a value from evaluate_displacement
use enclosing namespaces in core lib
use finer control over rtree instantiation
c file io wrapper: no need for explicit move + reset seek after checking size in ctor
use c file io wrapper in geojson/topojson plugins
python tests: remove either paths.py data or env settings for fonts/plugins
sync code between geojson and topojson rtree impl
break out topojson parsing grammar