Fix build on Xcode6

SDWebImage/SDWebImageDownloaderOperation.m

@@ -11,7 +11,10 @@
 #import "UIImage+MultiFormat.h"
 #import <ImageIO/ImageIO.h>
 
-@interface SDWebImageDownloaderOperation ()
+@interface SDWebImageDownloaderOperation () {
+    BOOL _executing;
+    BOOL _finished;
+}
 
 @property (copy, nonatomic) SDWebImageDownloaderProgressBlock progressBlock;
 @property (copy, nonatomic) SDWebImageDownloaderCompletedBlock completedBlock;
@@ -173,12 +176,22 @@
     [self didChangeValueForKey:@"isFinished"];
 }
 
+- (BOOL)finished
+{
+    return _finished;
+}
+
 - (void)setExecuting:(BOOL)executing {
     [self willChangeValueForKey:@"isExecuting"];
     _executing = executing;
     [self didChangeValueForKey:@"isExecuting"];
 }
 
+- (BOOL)executing
+{
+    return _executing;
+}
+
 - (BOOL)isConcurrent {
     return YES;
 }