Fixes T10057. Root issue is:

• In the past, you could give tokens to objects of type X (here, Ponder answers).
• Now, you can't.
• If you try to load a token on an object of type X, we do a bad call to attach it and fatal.

Instead, make sure objects implement the proper interface before we attach them, and just pretend the token does not exist otherwise.

Faked the exception in T10057, applied patch, got clean tokens page.