[TIMOB-8714] Android: 'focus' events are not correctly handled for windows in a tabGroup

// app.js
var tabGroup = Titanium.UI.createTabGroup();

var win1 = Titanium.UI.createWindow({  
    title:'Tab 1',
    backgroundColor:'#fff',
    url:'win1.js'
});

var tab1 = Titanium.UI.createTab({  
    icon:'KS_nav_ui.png',
    title:'Win 1',
    window:win1
});

var win2 = Titanium.UI.createWindow({  
    title:'Tab 2',
    backgroundColor:'#fff',
    url:'win2.js'
});

var tab2 = Titanium.UI.createTab({  
    icon:'KS_nav_ui.png',
    title:'Win 2',
    window:win2
});

tabGroup.addTab(tab1);
tabGroup.addTab(tab2);

tabGroup.open();

// win1.js
var win1 = Ti.UI.currentWindow;

win1.addEventListener('focus',function(e){
	alert('test win1');
});

// win2.js
var win2 = Ti.UI.currentWindow;

win2.addEventListener('focus',function(e){
	alert('test win2');
});