Removes references to now unused hiddenCellCache
Fixes iOS 6 bug where keyboard would remain but not be dismissible if active cell is scrolled off the top of the screen. Behaviour changes to dismiss keyboard when active cell is scrolled off the top of the screen. Updates comment to reflect change.
Keyboard will now dismiss when user begins dragging the TableView rather than when the active cell is moved offscreen.
Merge commit '4fe5842e9fd9bb5574d149a9a185be45fe81fd87'