FlxCamera memory leak

Memory leak in FlxCamera. For example:

```
var i : int = 100;
while(i--) {
    var cam:FlxCamera = new FlxCamera(0,0,FlxG.width,FlxG.height);
    FlxG.addCamera(cam);
    FlxG.removeCamera(cam, true);
}
```

After this code in stage create memory usage over 100 mb. Also work with FlxG.resetCameras();
