ForumNG - 'view posts by user' fails for clone forums (Bug 10979)

The original Forum called 'Shared_ForumNG' is on B201-10B and I have shared
this forum with DSE232-10I and K101-10J.
The view posts by user is now working for the original forum and the shared
forum on K101-10J. But it is still not working for the DSE232-10I course. Still
gives a no permissions error message.

I see why this is happening. Unfortunately I think the only way we can properly
fix it is to disable the 'view posts by user' feature for shared forums, which
kind of sucks seeing we nearly made it work but I think we can't get past
nearly...

Ray, please could you:

1) Change the code for showing the button, so that it does not show the button
for shared forums.

2) For consistency/security, change the list.php and user.php scripts so that
they fail (just throw an exception I guess, no need for a detailed error
message) if the forum is shared.