Clear scroll view delegate on dealloc.

Saw a crash on iOS 6 at
-[UIScrollView(UIScrollViewInternal) _delegateScrollViewAnimationEnded],
guessed at the cause.
Fix crash opening thread on iOS 5.

UIAccessibilityTraitHeader doesn't exist on iOS 5; loading it causes a crash.
Fix zero-width thread title on iOS 5.
Add logging around -[AwfulForumsListController toggleFavorite:].

Gotta find that crash!
Fix crash on iOS 5.1.

UIWebView doesn't like clearing the defaults.