Gentoo test harness improvements

Hello,

I'm sending you two more changes coming from Gentoo to improve the test system.

The first replaces RDiscount with kramdown so that it doesn't rely on a C-based extension, which is useful for supporting JRuby; the other removes some of the boilerplate from the test_app, including the dependencies over coffee-script, uglifier and sass-rails.

HTH,
Diego