throw exception when minifying font-awesome V4.3.0 css

[areel]

Using bundle-sfx on an app that includes font-awesome.

underlying issue is probably related to
clean-css/clean-css#524.

while investigating this (I haven't read the code closely) I thought it might be useful if the css plugin checked if the file referenced was already minified. This would allow imports statements like:

import 'font-awesome/css/font-awesome.min.css!';

Aidan

[guybedford]

Sure, I'll look into this when I can. Any suggestions are welcome too.

[areel]

Took another look and the bundle command reports the same error, Bootstrap is also failing

Steps to reproduce

jspm init -y
jspm install css bootstrap 
echo "import _ from 'bootstrap/css/bootstrap.css!';" > app.js
jspm bundle app app-build.js

I tested with the latest version of clean-css(3.3.2) (we are locked on 3.1) issue remains.