Conflicts: lib/groupnoticestream.php lib/taggedprofilenoticestream.php
Added filtering code so that notice streams check notice scope. Added new class to implement filtering a stream, FilteringNoticeStream. Added a subclass that does the logic for checking Notice scope. And made all the streams use ScopingNoticeStream.
* superfluous whitespace removed.
Rearchitect (again!) notice stream code to delegate different functionality up and down the stack. Now, different classes implement NoticeStream.
