Bug#16056813-MEMORY LEAK ON FILTERED SLAVE

Due to not resetting a member (last_added) of 
Deferred events class inside a clean up function
(Deferred_log_events::rewind), there is a memory
leak on filtered slaves.

Fix:
Resetting last_added to NULL in rewind() function.

sql/rpl_utility.cc:
  Resetting last_added to NULL to avoid memory leak

sql/rpl_utility.cc

@@ -1117,6 +1117,7 @@ void Deferred_log_events::rewind()
       Log_event *ev= *(Log_event **) dynamic_array_ptr(&array, i);
       delete ev;
     }
+    last_added= NULL;
     if (array.elements > array.max_element)
       freeze_size(&array);
     reset_dynamic(&array);