[UI] Fix TTTableViewController resize for keyboard bug

Hi,

This fixes TTTableViewController resize for keyboard not working for tableviews that are not reaching the bottom of the screen (when there's a tabbar or toolbar for instance).

This was originally submitted as part of the fixes in https://github.com/facebook/three20/pull/307

To make it easier for you to merge it, it is now based off the facebook:development branch.

Thanks