Fix now() when USE_TZ is turned off in Django 1.5

Django 1.5 changes the contract of timezone.localtime (which was
previously undocumented) such that it must be provided with a timezone
aware datetime object. timezone.now() only returns a timezone aware
object when USE_TZ is enabled, so when USE_TZ is not set it is not
safe to call timezone.localtime() on the result.