The reason polymorphic broke was because it couldn't find some managers
anymore in the inheritance tree. Django 1.5 removes these and replaces
them with an `AbstractManagerDescriptor`. This patch restores those objects
- by default, django_polymorphic's pretty printing of querysets/objects (via ShowField*) is not used anymore
- ShowField mixins now also show the annotations (after the regular fields, prepended by "Ann:")
- cleaned up implementation.
- added python2.4 compatibility. Contributed by Charles Leifer. Thanks!
- general reorganization of the code - there is no single polymorphic.py module anymore,
so d-p now needs to be installed as a regular Django app
- polymorphic.VERSION/get_version added
- version numbering started: V0.5 beta