Some spec cleanup.
Improve Rails 4 gem support.

Do not put asset-related gems in Bundler 'asset' group (due to change in
how Rails 4 wants this.) Also, use the alpha version of Compass, which
has support for Rails 4.
Make routes work for Rails 4.

Needed to keep Rails 3 compatability in mind also.
Add coderay to precompile list.
Add turbo-sprockets-rails3 for Rails 3 apps.

Speeds up their asset precompilation by at least double on first run,
even faster on subsequent runs.