option to exclude certain names from mangling

lib/scope.js

@@ -354,7 +354,8 @@ AST_LoopControl.DEFMETHOD("target", function(){
 
 AST_Toplevel.DEFMETHOD("mangle_names", function(options){
     options = defaults(options, {
-        sort: false
+        sort   : false,
+        except : []
     });
     // We only need to mangle declaration nodes.  Special logic wired
     // into the code generator will display the mangled name if it's
@@ -376,8 +377,11 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
             var a = node.variables;
             for (var i in a) if (HOP(a, i)) {
                 var symbol = a[i];
-                if (!(is_setget && symbol instanceof AST_SymbolLambda))
-                    to_mangle.push(symbol);
+                if (!(is_setget && symbol instanceof AST_SymbolLambda)) {
+                    if (options.except.indexOf(symbol.name) < 0) {
+                        to_mangle.push(symbol);
+                    }
+                }
             }
             return;
         }
@@ -385,7 +389,7 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
             var name;
             do name = base54(++lname); while (!is_identifier(name));
             node.mangled_name = name;
-            return;
+            return true;
         }
     });
     this.walk(tw);