rs/SDWebImage — pull request #595 by jiwanqiang (2013-12-31 12:58:45+00:00)
Title: fix bug (global configure for downloader)

When used the SDWebImageManager class, we need configure the cache and downloader. In order to implement it, we need global configure.
Like this:
SDWebImageDownloader.sharedDownloader.maxConcurrentDownloads = 12;
SDWebImageDownloader.sharedDownloader.executionOrder = SDWebImageDownloaderLIFOExecutionOrder;
....
So that, in anywhere we call the functions to set image, it can be delivered immediately.