Fix crashes on iOS 5.

NSFetchedResultsController manages to hang around on iOS 5 and will try to send
to its delegate after said delegate gets deallocated..
Deselect thread cells on tap.

They deselect when the table view disappears from view, so this omission went
unnoticed until the "keep sidebar open" option appeared.
Remove redundant setting for bookmarked threads.

The isBookmarked value gets applied from the parsed info.
Fix star color parsing for bookmarked threads.

Changed in the New Year's forum update; managed to miss it due to shitty tests.