Prevent MySQL has gone away errors (#58)

Prevents Error "MySQL has gone away" when Django tries to go through old, timed-out or closed connections.
After calling close_old_connections() Django opens a new connection if the old one was closed.

Author: bigmars86

django_celery_beat/schedulers.py

@@ -13,7 +13,7 @@
 from celery.utils.log import get_logger
 from kombu.utils.json import dumps, loads
 
-from django.db import transaction
+from django.db import transaction, close_old_connections
 from django.db.utils import DatabaseError
 from django.core.exceptions import ObjectDoesNotExist
 
@@ -232,6 +232,7 @@ def sync(self):
         info('Writing entries...')
         _tried = set()
         try:
+            close_old_connections()
             with transaction.atomic():
                 while self._dirty:
                     try: