trace: Send task_failure signal

celery/execute/trace.py

@@ -124,4 +124,8 @@ class TaskTrace(object):
         einfo = ExceptionInfo((type_, exc, tb))
         self.task.on_failure(exc, self.task_id,
                              self.args, self.kwargs, einfo=einfo)
+        signals.task_failure.send(sender=self.task, task_id=self.task_id,
+                                  exception=exception, args=self.args,
+                                  kwargs=self.kwargs, traceback=tb,
+                                  einfo=einfo)
         return einfo

celery/signals.py

@@ -147,7 +147,7 @@ Worker Signals
 
 .. data:: worker_init
 
-    Dispatched beforee the wxorker is started.
+    Dispatched before the worker is started.
 
 .. data:: worker_ready