rs/SDWebImage — pull request #987 by morizotter (2014-12-16 02:16:07+00:00)
Title: Fix NSNotificationCenter dispatch on subthreads.

In currently version, `SDWebImageDownloaderOperation`'s notifications are dispatched on multiple threads. Considering notifications are global and supposed to be used for other purposes, dispatching on main thread seems to be better. UIApplication's `setNetworkActivityIndicatorVisible:` in `SDNetworkActivityIndicator` seems to be better to execute on main thread ,too.