autoprefixer test: Switch to unexpected.
Converted buildDevelopment test to mocha and unexpected.
Update assetgraph to 1.6.22.
unexpected-with-plugins: More sugar.
Implemented duplicateFavicon transform.
buildProduction: Don't move .htaccess, humans.txt, robots.txt, or favicon.ico to the static dir.

See assetgraph/assetgraph#185.