r212: Fixed a problem where the last post would be off if we did not have permission...

r212: Fixed a problem where the last post would be off if we did not have permission to see the comment. Quite a big fix. What was done is a `bug.hiddenlastposttime` and a `bug.hiddenlastpostby` were created and these track the last unhidden comment. The originals still track all of them, though. Therefore whenever a comment is modified or added, this record is updated to the most recent unhidden comment.