refs #431: bring back Travis Bash strictness
update mapbox/variant
use texsubimage2d to avoid texture memory reallocation
add missing git fetch for mapnik-packaging

When there is a local mapnik-packaging repo,
git checkout a future commit requires a git fetch
bring back Linux tests in separate script
rename tests script
Rename existing interpolate -> resample
Consolidate duplicate interpolation definitions

While here, do not interpolate style properties that
are not transitionable. The previous behavior was to
switch from old to new value halfway through the transition;
now the new value is used immediately, as in JS.
Load TileJSON; support inline TileJSON sources

Fixes #412
Refs https://github.com/mapbox/mapbox-gl-style-spec/pull/143
Use float for pixelRatio
Indicate gzip support as well as deflate

libcurl supports both: http://curl.haxx.se/dev/readme-encoding.html
Fix headless tests
add basic request caching with sqlite
remove access token from URL
also store other response codes in the cache
compress data and store type