提升Xcode5里6.1模拟器的速度
2014-02-18打开Xcode5的模拟器，切换到7.0之前的系统，比如6.1，就会发现里面的应用会一卡一卡的。在Xcode5.1beta版的release notes里面有关于这个的说明：
Developers may experience performance issues when running apps within the iOS Simulator on Mavericks with a simulated OS version of iOS 6.1 or earlier. The suggested workaround for this issue is to disable timer coalescing while using the iOS 6.1 or earlier simulator. (15501929):
sudo sysctl -w kern.timer.coalescing_enabled=0
另外关于键盘偶尔不能使用的问题：
The iOS simulator sometimes stops responding to hardware keyboard. Usually, quitting and relaunching the simulator will correct this. (14642684)