Xcode7.3 iOS 9报错
：This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
原因是在线程中做了页面跳转；－－UI处理全部都要放到主线程中；
Applications/Xcode.app/Contents/Developer/usr/bin/copypng emitted errors but did not return a nonzero exit code to indicate failure
原因：要么图片格式不正确，要么图片重复
