Retain asset query and fragment when generating hashed url

Resolves https://github.com/middleman/middleman/issues/1024

With `asset_hash` and `asset_host` enabled, `font-url('glyphs.eot?#iefix")` will now yield something like `/fonts/glyphs-a3d23.eot?#iefix`
`font-url` should be unnecessary for these tests, the hash rewriter works directly on rendered output. Can you change this to a hard-coded path, remove sprockets, and see if the other issues with the tests resolve?