Merge pull request #1504 from siburb/master

Added "cancelAllDownloads" method to SDWebImageDownloader.

SDWebImage/SDWebImageDownloader.h

@@ -188,4 +188,9 @@ typedef NSDictionary *(^SDWebImageDownloaderHeadersFilterBlock)(NSURL *url, NSDi
  */
 - (void)setSuspended:(BOOL)suspended;
 
+/**
+ * Cancels all download operations in the queue
+ */
+- (void)cancelAllDownloads;
+
 @end

SDWebImage/SDWebImageDownloader.m

@@ -229,4 +229,8 @@ static NSString *const kCompletedCallbackKey = @"completed";
     [self.downloadQueue setSuspended:suspended];
 }
 
+- (void)cancelAllDownloads {
+    [self.downloadQueue cancelAllOperations];
+}
+
 @end