Fix several navigation bar glitches in iOS 7.1.

* After popping, back button arrows appear on the navigation bars (even though they don't have titles and aren't tappable.)
* On the first pop of the right view controller, an ellipsis follows the new right navigation bar title in as it transitions in from the left (though the ellipsis disappears as soon as the animation completes.)
* On the first push of a left view controller, an ellipsis follows the new navigation bar title in as it transitions in from the left (though the ellipsis disappears as soon as the animation completes.)
* When pushing a new view controller after both sides already have view controllers, the right navigation bar title disappears during the transition.
* An ellipsis sometimes appear when fake navigation items are used unless the item has an empty, rather than nil, title.
Merge pull request #13 from jcoleman/fix-gimpy-back-buttons-in-ios7

Fix several navigation bar glitches in iOS 7.1.