Implement -m sort=true

close #83

lib/scope.js

@@ -340,6 +340,7 @@ AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
     return defaults(options, {
         except : [],
         eval   : false,
+        sort   : false
     });
 });
 
@@ -360,12 +361,16 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
             return true;        // don't descend again in TreeWalker
         }
         if (node instanceof AST_Scope) {
-            var p = tw.parent();
+            var p = tw.parent(), a = [];
             node.variables.each(function(symbol){
                 if (options.except.indexOf(symbol.name) < 0) {
-                    to_mangle.push(symbol);
+                    a.push(symbol);
                 }
             });
+            if (options.sort) a.sort(function(a, b){
+                return b.references.length - a.references.length;
+            });
+            to_mangle.push.apply(to_mangle, a);
             return;
         }
         if (node instanceof AST_Label) {