Add test case to isolate collision error in grid renderer.
Pass recentered transform to markers_placement_finder in vector_markers_rasterizer_dispatch_grid. Update expected grids for test case.
Update other affected test grids from recenter fix in grid markers helper.
fix back compat for text-placement-type:dummy - closes #2502
Merge pull request #2501 from MapQuest/grid_markers_fix

Grid markers fix for issue #2500
fix line symbolizer 'rasterizer' property - closes #2503
comment debug code
start more font reg/cache tests
higher grid tolerance, even for OS X
text_properties code cleanup - pregame for #2504
scons: fix memory leak in configure test
dodge #2505 by avoiding registering gdal/ogr plugin
visual test coverage of shield-text-opacity/text-opacity - refs #2507
fix handling of shield-text-opacity/text-opacity - closes #2507
warn if duplicate attribute - closes #2508
drop useless template usage for has_key
fix font caching logic
better rules names
throw std::runtime_error on expectation failure
completely purge buggy osm plugin from visual tests