Show number of syncing entries in the log (#481)

* Show number of syncing entries in the log

Useful for debugging purposes; it's nice to know whether any tasks are actually being sync'ed.

* Lazy eval of log message

Author: chrisclark

djcelery/schedulers.py

@@ -198,7 +198,7 @@ def reserve(self, entry):
         return new_entry
 
     def sync(self):
-        info('Writing entries...')
+        info('Writing entries (%s)...', len(self._dirty))
         _tried = set()
         try:
             with commit_on_success():