干掉xcode 4.2里的performselector警告

xcode 4.2非常可恶，原来的代码里有调用performselector:withObject:的地方无一例外获得一个警告：

Semantic Issue
PerformSelector may cause a leak because its selector is unknown

warning倒是不影响程序运行，但是这人要是有点代码小洁癖的话，那日子就没法过了，这warning怎么看都碍眼。所以必须得想办法把它弄没了：

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    [self performSelector:nextView];
#pragma clang diagnostic pop