admin: close db connection around fork

When forking database connection status is incertain, so we explicitely
close it. Django will reopen it.

portail_citoyen_announces/admin.py

@@ -2,6 +2,7 @@ import os
 
 from django.contrib import admin
 from django.contrib.sites.models import get_current_site
+from django.db import connection
 
 import models
 import transports
@@ -23,7 +24,9 @@ class SendingAction(object):
     def __call__(self, modeladmin, request, queryset):
         pid = os.fork()
         if pid != 0:
+            connection.close()
             return
+        connection.close()
         transport = transports.get_transport(self.mode)
         for announce in queryset.select_related():
             transport.send(announce)