Run tests using http requests

We now start a local HTTP server on port 2900 that serves the test fixtures. This is the same port we also use in the JS test suite

fixes #532
pass array with a single nullptr instead of nullptr for compatibility
replace strftime_l with our custom formatter
use execv and pass non-inline argument for gcc
use dirname() on copies of the parameter only

glibc's dirname() modifies the parameter
add basic toupper/tolower text conversions tests #309
format
Merge pull request #540 from mapbox/test-http

Run tests using HTTP requests
also use custom formatter for OS X
line-offset -> line-gap-width
More concise
Axe the 16-px line width limit
v6: min-zoom -> minzoom, max-zoom -> maxzoom
Reinstate 16px line width limit
Implement v6 filters
Use v6 styles
Update styles
Render ⇢ layout, style ⇢ paint

https://github.com/mapbox/mapbox-gl-style-spec/issues/166
Single text positioning property

https://github.com/mapbox/mapbox-gl-style-spec/issues/197
Support compound text-anchor values