Fix for iOS 7.
Fix for iOS 7.

The new date and time picker does not appear on a black background.

jstedfast/MonoTouch.Dialog,benoitjadinon/MonoTouch.Dialog,Milan1992/MonoTouch.Dialog,newky2k/MonoTouch.Dialog,migueldeicaza/MonoTouch.Dialog,hisystems/MonoTouch.Dialog,ClusterReplyBUS/MonoTouch.Dialog,danmiser/MonoTouch.Dialog