[AC-560] Setting backgroundColor on a Ti.UI.Button causes it to lose default styling of border radius & active state

By default, Android buttons are have grey background, white text, round corners, a drop shadow and circular animation effect when tapped. I would expect when setting the backgroundColor, the button would retains borderRadius and active state animation. Instead, setting a backgroundColor causes the button to lose the rounded corners & active animation effect. Test case:

var win1 = Ti.UI.createWindow({
    title:'Button test',
    backgroundColor:'#fff'
});
var button = Ti.UI.createButton({
    //backgroundColor: "red", // uncomment to lose borderRadius + active effect
    title: "Click me"
});

win1.add(button);
win1.open();