better environment detection

lib/less/parser.js

@@ -1,23 +1,10 @@
-var less, tree, charset;
+var less, tree;
 
-if (typeof environment === "object" && ({}).toString.call(environment) === "[object Environment]") {
-    // Rhino
-    // Details on how to detect Rhino: https://github.com/ringo/ringojs/issues/88
-    if (typeof(window) === 'undefined') { less = {} }
-    else                                { less = window.less = {} }
-    tree = less.tree = {};
-    less.mode = 'rhino';
-} else if (typeof(window) === 'undefined') {
-    // Node.js
-    less = exports,
+// Node.js does not have a header file added which defines less
+if (less === undefined) {
+    less = exports;
     tree = require('./tree');
     less.mode = 'node';
-} else {
-    // Browser
-    if (typeof(window.less) === 'undefined') { window.less = {} }
-    less = window.less,
-    tree = window.less.tree = {};
-    less.mode = 'browser';
 }
 //
 // less.js - parser