App: Be sure to pickle _preconf for Windows if the app is not configured when pickling. Closes #897

Conflicts:
	celery/app/base.py

celery/app/base.py

@@ -538,7 +538,7 @@ class Celery(object):
         when unpickling."""
         return {
             'main': self.main,
-            'changes': self.conf.changes,
+            'changes': self.conf.changes if self.configured else self._preconf,
             'loader': self.loader_cls,
             'backend': self.backend_cls,
             'amqp': self.amqp_cls,