Add a warning message when a entire stylesheet could not be parsed

lib/metadata/policies.js

@@ -403,7 +403,7 @@ var policies = {
 
                     if (parts) {
                         return {
-                            error: parts[2] || 'Unknown parsing error',
+                            error: parts[2] || 'Unknown parsing error' + (parts[1] ? '. The entire file was ignored. As a result, the other CSS metrics and scores are miscalculated.' : ''),
                             file: parts[1] || null,
                             line: (parts[4] && parts[5]) ? parseInt(parts[4], 10) : null,
                             column: (parts[4] && parts[5]) ? parseInt(parts[5], 10) : null