Fix for :debug_assets

When :debug_assets is on, prevent "?body=1" from being appended multiple times to a script tag. This will eventually cause a browser error because of the enormous URL.

Screenshot of the bug is attached.

![screenshot](https://f.cloud.github.com/assets/659307/508431/7704eb10-bd87-11e2-8182-5b39d05cecfd.png)