Refactor tile cover to match JS
Support pixelRatio parameter for render tests
transition-* ⇢ *-transition

https://github.com/mapbox/mapbox-gl-style-spec/issues/148
add debugging
move make_active call into MBGL_USE_CGL block
Merge branch 'master' into libuv010
Merge branch 'libuv010' into libuv-0.10-fix-context-shutdown

Conflicts:
	common/headless_view.cpp
	test/headless.cpp