[AC-3041] iOS Titanium.UI.Window with titleControl does not reliably display rightNavButton on iPhone 4 device (not in simulator!)

In our app we use windows (Titanium.UI.Window) which are themed with a barImage and have a titleControl (Titanium.UI.Label) in order to style the title. The windows are organized via tabgroups where per tab window additional windows are opened with animation. During several cycles of open -> close -> open -> close suddenly the rightNavButton disappears and appears again if the orientation of the device is changed (portrait -> landscape -> portrait). This only happens on a real device not in simulator! Further inverstigations revealed that this is due to the workarraound in line #321 of TiUIWindowProxy.m for iOS 5: [https://github.com/appcelerator/titanium_mobile/blob/master/iphone/Classes/TiUIWindowProxy.m#L321] which has been created before GA of the iOS 5 SDK. If this workarround is replaced by the correct native implementation (setBackgroundImage) the bug is gone. You'll find attached a context diff with a proposed implementation which solved the bug. Please consider applying the attached patch to master and branch/1.8.0.1. Regards.