Pass source file name to coffee compiler.

@josh Working from your `coffee-script-sourcemap` branch, this passes the original file name along to the coffee compiler so it will add it to the the source map’s `sources` array. Then we can map the compiled js back to its original coffee file.
The value of `input[:name]` does not include the `.coffee` extension. It's a bare name for the file's logical path, like `"search/api"`. Should we add the `.coffee` extension to it here?