Tasks list as result for completionOfAllTasks api.

Created by: OdNairy

We had a nil result from completionOfAllTasks for the all time. It will be very helpful to have tasks list in next "bolt". We can found the same idea on the Facebook's Parse.Promise and PromiseKit as well.

P.S. New functionality test have been added and CLA have been signed.

Bolts/Common/BFTask.m

@@ -122,7 +122,7 @@ __attribute__ ((noinline)) void warnBlockingOperationOnMainThread() {
                         tcs.error = error;
                     }
                 } else {
-                    tcs.result = nil;
+                    tcs.result = tasks;
                 }
             }
             return nil;

BoltsTests/TaskTests.m

@@ -235,6 +235,30 @@
     XCTAssertTrue(task.isCancelled);
 }
 
+- (void)testTaskForCompletionOfAllTasksResult {
+    NSMutableArray *tasks = [NSMutableArray array];
+    
+    const int kTaskCount = 20;
+    for (int i = 0; i < kTaskCount; ++i) {
+        double sleepTimeInMs = rand() % 100;
+        [tasks addObject:[[BFTask taskWithDelay:sleepTimeInMs] continueWithBlock:^id(BFTask *task) {
+            return @(i);
+        }]];
+    }
+    
+    [[[BFTask taskForCompletionOfAllTasks:tasks] continueWithBlock:^id(BFTask *task) {
+        XCTAssertEqual(task.result, tasks);
+        XCTAssertNil(task.error);
+        XCTAssertNil(task.exception);
+        XCTAssertFalse(task.isCancelled);
+        
+        for (int i = 0; i < kTaskCount; ++i) {
+            XCTAssertEqual(i, [((BFTask *)[task result][i]).result intValue]);
+        }
+        return nil;
+    }] waitUntilFinished];
+}
+
 - (void)testTaskForCompletionOfAllTasksSuccess {
     NSMutableArray *tasks = [NSMutableArray array];