iOS 5 ipad compatibility issues

 this pull request includes some changes to TTBaseController which solves the issues with UIPopViewController & TTSplitViewController under iOS 5.

The parentViewController function role was under with iOS 5 (http://omegadelta.net/2011/11/04/oh-my-god-they-killed-parentviewcontroller/) which caused issues with TTSplitViewController when the secondary view controller is displayed as a popup view controller.

closes #713