Warn that Generic Relations are a prototype feature (in the right places).

[enlight]

There was a thread on django-users recently ("GenericRelation and serialization") where Russell Keith-Magee wrote:
"GenericRelations are a bit of a wierd case - they're available in Django, but they're still a prototype feature - they're not fully documented, and they're not as well tested as other aspects of Django."

This was a bit of a shock to me, I knew they were barely documented, but I didn't realise they were a prototype feature. Since I didn't recall any such warning in the scarce documentation on generic relations - I went looking for it, sure enough I found it at the end of the "Branches in development" section over on this page ​http://code.djangoproject.com. That explains why I didn't recall it, I wasn't expecting any of the text in that section to apply to the trunk.

The warning should really be moved to the following places where I would've actually noticed and paid attention to it:

​http://code.djangoproject.com/browser/django/trunk/django/db/models/fields/generic.py
and
​http://www.djangoproject.com/documentation/models/generic_relations/

I'll see about creating a patch for this tomorrow.

[Malcolm Tredinnick]

It's better that we fix the real problem here: which is moving generic relation to their right home in the source tree. That will be done soon. The current instability in the API is documented in api-stability.txt.