CSS sprockets debug Fix for https://github.com/middleman/middleman-sprockets/issues/28

1 failed test at cucumber features/asset_hash.feature:56 # Scenario:
Enabling an asset host still produces hashed files and references.

Don't work when filename is the same as js. For example app.js app.css,
then when in tags options are "app" and "app" then sprockets load
everytime js files.

Fix for https://github.com/middleman/middleman-sprockets/issues/28