Breaks Panels module

Hello,

There's an issue with username_check_auto.js in that it is breaking the javascript code within the Panels module's edit panel content screen. It happens when one is using the user_register form as a Fieldset context, which fires off hook_form_alter on user_register which results in the javascript being incorrectly attached.

I just went and put the first bit inside a try/catch block and it works fine. Patch attached..