add block_scope to --output ast (#2780)

bin/uglifyjs

@@ -268,6 +268,11 @@ function run() {
                 var result = {
                     _class: "AST_" + value.TYPE
                 };
+                if (value.block_scope) {
+                    result.variables = value.block_scope.variables;
+                    result.functions = value.block_scope.functions;
+                    result.enclosed = value.block_scope.enclosed;
+                }
                 value.CTOR.PROPS.forEach(function(prop) {
                     result[prop] = value[prop];
                 });