fix for VirtualPages error

It seems VirtualPages are not able to resolve isFrontend calls when
Fluent asks them too. The result of this is:

```
Undefined property: VirtualPage::$CopyContentFromID
Line 70 in /home/jwss/public_html/.ss3/cms/code/model/VirtualPage.php

Trace
VirtualPage->CopyContentFrom()
call_user_func_array(Array,Array)
Object.php:729
Object->__call(CopyContentFrom,Array)
VirtualPage.php:533
VirtualPage_Controller->__call(CopyContentFrom,Array)
VirtualPage.php:513
VirtualPage_Controller->CopyContentFrom()
VirtualPage.php:513
VirtualPage_Controller->hasMethod(isFrontend)
Fluent.php:308
Fluent::is_frontend()
```

the problem seems to go away when I tell Fluent.php NOT to call
the isFontend method on a VirtualPage_Controller.