The change introduced by #82, which is commit 9d0097d, is too aggressive.
There are a few problems with this:
The bigger problem, a url() is not neccesarily a local file. For example, if I want to use Google web fonts, my CSS file has the line
which is neither an image file nor a local file.
If you intend on using Google Web Fonts you could still download the fonts and load them locally to circumvent this problem.