优化PhoneGAP的Splashscreen

基于PhoneGap 2.0.0 源码版本，修改了 Commands 包下的 CDVSplashScreen 类，使用 Splashscreen的过度效果更自然，以下代码只是抛砖引玉，可以利用ios的动画库实现更多的过度动画，如：为Splashscreen增加一个按钮等。

- (void) __show:(BOOL)show
{
    // Legacy support - once deprecated classes removed, clean this up
    id<UIApplicationDelegate> delegate = [[UIApplication sharedApplication] delegate];
    
    if ([delegate respondsToSelector:@selector(viewController)]) {
        id vc = [delegate performSelector:@selector(viewController)];
        if ([vc isKindOfClass:[CDVViewController class]]) {
            [UIView beginAnimations:nil context:nil];
            [UIView setAnimationDuration:0.9];
            [UIView setAnimationTransition:UIViewAnimationTransitionNone forView:((CDVViewController*)vc).view cache:YES];
            [UIView setAnimationDelegate:((CDVViewController*)vc)];
　　　　　　　// 动画结束后执行隐藏操作
            [UIView setAnimationDidStopSelector:@selector(showAnimationDone:vc:show:finished:context:)];
            ((CDVViewController*)vc).imageView.alpha = 0.0;//让Splashscreen 的填充图片的透明度渐渐变为0;
            ((CDVViewController*)vc).activityView.alpha = 0.0; //让Splashscreen 的活动视图的透明度渐渐变为0;
            [UIView commitAnimations];
        }
    }
}

//动画结束后隐藏Splashscreen
- (void) showAnimationDone:(id*)viewController showOrhide:(BOOL)show animationID:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context
{
    ((CDVViewController*)viewController).imageView.hidden = !show;
    ((CDVViewController*)viewController).activityView.hidden = !show;
}