Synchronize access to SDWebImageManager's mutable structures (fix #301)

@@ -83,7 +83,10 @@
         return operation;
     }
 
+    @synchronized(self.runningOperations)
+    {
         [self.runningOperations addObject:operation];
+    }
     NSString *key = [self cacheKeyForURL:url];
 
     [self.imageCache queryDiskCacheForKey:key done:^(UIImage *image, SDImageCacheType cacheType)
@@ -93,8 +96,11 @@
         if (image)
         {
             completedBlock(image, nil, cacheType, YES);
+            @synchronized(self.runningOperations)
+            {
                 [self.runningOperations removeObject:operation];
             }
+        }
         else
         {
             SDWebImageDownloaderOptions downloaderOptions = 0;
@@ -108,9 +114,12 @@
                 {
                     if (error.code != NSURLErrorNotConnectedToInternet)
                     {
+                        @synchronized(self.failedURLs)
+                        {
                             [self.failedURLs addObject:url];
                         }
                     }
+                }
                 else if (downloadedImage && finished)
                 {
                     const BOOL cacheOnDisk = !(options & SDWebImageCacheMemoryOnly);
@@ -119,8 +128,11 @@
 
                 if (finished)
                 {
+                    @synchronized(self.runningOperations)
+                    {
                         [self.runningOperations removeObject:operation];
                     }
+                }
             }];
             operation.cancelBlock = ^{[subOperation cancel];};
         }
@@ -131,8 +143,11 @@
 
 - (void)cancelAll
 {
+    @synchronized(self.runningOperations)
+    {
         [self.runningOperations makeObjectsPerformSelector:@selector(cancel)];
         [self.runningOperations removeAllObjects];
+    }
 }
 
 - (BOOL)isRunning