The Manual Updates page tried to load the JS catalog, needed in order to

expose gettext() for the other scripts being loaded. That path wasn't

explicitly allowed, resulting in HTML being sent back as the script

contents, causing the browser to show some errors.
We may want to consider just blocking off all script loading. That will

require blocking extensions as well, though, and possibly daeling with

other corner cases. In the meantime, allow the JS catalog to be loaded.

First saw this on my local install before upgrading the version in the

DB to RC 3. After the fix, I no longer saw a series of JavaScript errors.