VecTiles: increase max zoom supported for pixel tolerances
VecTiles: add support to pad tile bounding box by a specified amount(used by OpenScienceMap to hide seams between tiles)
moves bounding box SQL construction to build_query function
drop null valued properties.
Merge branch 'add-opensciencemap-vectiles' into integration-1

Conflicts:
	TileStache/Goodies/VecTiles/server.py
Merge pull request #9 from mapzen/drop-null-val-prop

Drop null valued properties
Merge branch 'integration-1' into add-layer-name-to-vtm-tiles

Conflicts:
	TileStache/Goodies/VecTiles/oscimap.py