clone ruleset before passing it to applyEmbeddedRuleset; fixes #458

since applyEmbeddedRuleset modifies the ruleset in-place,
this ensures that those modifications aren't visible to the caller

Author: cvrebert

src/core/CSSLint.js

@@ -5,7 +5,7 @@
  * @extends parserlib.util.EventTarget
  */
 
-/* global parserlib, Reporter */
+/* global parserlib, clone, Reporter */
 /* exported CSSLint */
 
 var CSSLint = (function(){
@@ -189,6 +189,8 @@ var CSSLint = (function(){
         }
 
         if (embeddedRuleset.test(text)){
+            //defensively copy so that caller's version does not get modified
+            ruleset = clone(ruleset);
             ruleset = applyEmbeddedRuleset(text, ruleset);
         }