make import visitor stack up frame scopes

lib/less/import-visitor.js

@@ -24,6 +24,35 @@
         visitRule: function (ruleNode, visitArgs) {
             visitArgs.visitDeeper = false;
             return ruleNode;
+        },
+        visitDirective: function (directiveNode, visitArgs) {
+            this.env.frames.unshift(directiveNode);
+            return directiveNode;
+        },
+        visitDirectiveOut: function (directiveNode) {
+            this.env.frames.shift();
+        },
+        visitMixinDefinition: function (mixinDefinitionNode, visitArgs) {
+            this.env.frames.unshift(mixinDefinitionNode);
+            return mixinDefinitionNode;
+        },
+        visitMixinDefinitionOut: function (mixinDefinitionNode) {
+            this.env.frames.shift();
+        },
+        visitRulesetDefinition: function (rulesetNode, visitArgs) {
+            this.env.frames.unshift(rulesetNode);
+            return rulesetNode;
+        },
+        visitRulesetDefinitionOut: function (rulesetNode) {
+            this.env.frames.shift();
+        },
+        visitMedia: function (mediaNode, visitArgs) {
+            this.env.frames.unshift(mediaNode.ruleset);
+            return mediaNode;
+        },
+        visitMediaOut: function (mediaNode) {
+            this.env.frames.shift();
         }
     };
+
 })(require('./tree'));

lib/less/visitor.js

@@ -25,6 +25,10 @@
             if ((!visitArgs || visitArgs.visitDeeper) && node && node.accept) {
                 node.accept(this);
             }
+            funcName = funcName + "Out";
+            if (this._implementation[funcName]) {
+                this._implementation[funcName](node);
+            }
             return node;
         },
         visitArray: function(nodes) {