This prevents collisions between boolean and integer values. In python:
1 == True and 0 == False. But, we don't want these to point to the same
value in the index table.
I kicked off a build on master to check, which matches the v1.2.0 tag, and travis fails on that too. I'll merge this in, and I created another issue to track fixing the failure.
Connects to https://github.com/tilezen/mapbox-vector-tile/issues/96
This prevents collisions between boolean and integer values. In python: 1 == True and 0 == False. But, we don't want these to point to the same value in the index table.