Merge pull request SDWebImage#588 from wishabi/master

Assign thread for downloada cancellation + minor doc fix

Author: Olivier Poitrey

SDWebImage/SDImageCache.h

@@ -91,7 +91,7 @@ typedef enum SDImageCacheType SDImageCacheType;
  *
  * @param image The image to store
  * @param recalculate BOOL indicates if imageData can be used or a new data should be constructed from the UIImage
- * @param data The image data as returned by the server, this representation will be used for disk storage
+ * @param imageData The image data as returned by the server, this representation will be used for disk storage
  *             instead of converting the given image object into a storable/compressed image format in order
  *             to save quality and CPU
  * @param key The unique image cache key, usually it's image absolute URL

SDWebImage/SDWebImageDownloaderOperation.m

@@ -85,6 +85,7 @@ - (void)start
 
         self.executing = YES;
         self.connection = [NSURLConnection.alloc initWithRequest:self.request delegate:self startImmediately:NO];
+        self.thread = [NSThread currentThread];
     }
 
     [self.connection start];