Protect all possibly-unset env vars
bump mapnik-packaging
Merge branch 'mphash-libuv-pkgconfig' into libuv-0.10-headless-display

Conflicts:
	setup-libraries.sh
Merge pull request #486 from mapbox/mphash-libuv-pkgconfig

bump mapnik-packaging
use node-mapbox-gl-native AWS bucket for travis caching
Merge branch 'master' into libuv-0.10-headless-display

Conflicts:
	setup-libraries.sh