Behave like CommonJS module in CommonJS context

src/peg.js

@@ -1,4 +1,4 @@
-(function(global) {
+(function() {
 
 var undefined;
 
@@ -32,6 +32,10 @@ PEG.GrammarError.prototype = Error.prototype;
 // @include "parser.js"
 // @include "compiler.js"
 
-global.PEG = PEG;
+if (typeof exports !== "undefined") { // Looks like we're in CommonJS environment.
+  extend(exports, PEG);
+} else {                              // Okay, assume this is a browser.
+  window.PEG = PEG;
+}
 
-})(this);
+})();

src/utils.js

@@ -1,3 +1,9 @@
+function extend(target, source) {
+  for (var key in source) {
+    target[key] = source[key];
+  }
+}
+
 function contains(array, value) {
   /*
    * Stupid IE does not have Array.prototype.indexOf, otherwise this function