Update core.py

flask login changed the name of the anonymous user object.
when run without this mod you will get 

  from flask.ext.security import url_for_security
  File "C:\Python27\lib\site-packages\flask\exthook.py", line 81, in load_module
    reraise(exc_type, exc_value, tb.tb_next)
  File "C:\Python27\lib\site-packages\flask_security\__init__.py", line 15, in <module>
    from .core import Security, RoleMixin, UserMixin, AnonymousUser, current_user
  File "C:\Python27\lib\site-packages\flask_security\core.py", line 13, in <module>
    from flask.ext.login import AnonymousUser as AnonymousUserBase, \
ImportError: cannot import name AnonymousUser