title: django-celery doesn't work with CONN_MAX_AGE
body: <p>I am using Django 1.6.5, celery 3.1.13 and django-celery 3.1.10.Django has a new configuration "CONN_MAX_AGE" for database pooling since 1.6, but the problem is, when I config the database without CONN_MAX_AGE, the celery works well. But if I set CONN_MAX_AGE to any value, the celery will report (OperationalError) (2006, 'MySQL server has gone away') and won't beat.</p>
  
  <p>My configuration is: </p>
  
  <pre><code>DATABASES = {
      'default': {
          'ENGINE': 'django.db.backends.mysql',
          'NAME': 'mydb',
          'USER': 'root',
          'PASSWORD': 'root',
          'HOST': 'localhost',
          'PORT': '3306',
          'CONN_MAX_AGE': 28000,  # if comment this line out, celery works well
      },
  }
  
  BROKER_URL = 'amqp://guest:guest@localhost:5672//'
  CELERY_RESULT_BACKEND = 'amqp'
  CELERY_SEND_EVENTS = True
  CELERY_TASK_RESULT_EXPIRES = 3600
  
  CELERYBEAT_SCHEDULER = 'djcelery.schedulers.DatabaseScheduler'
  CELERYBEAT_MAX_LOOP_INTERVAL = 60
  CELERY_IMPORTS = ('library.task',)
  
  import djcelery
  
  djcelery.setup_loader()
  </code></pre>
  
  <p>Then run celery with</p>
  
  <pre><code>python manage.py celeryd -B -lDEBUG
  </code></pre>
  
  <p>How to solve this problem?</p>