Track ongoing deprecation

[xordoquy]

While we have a deprecation policy, we don't track the ongoing deprecations.
We need to have something similar to https://docs.djangoproject.com/en/1.8/internals/deprecation/ to help us conform to the policy.

[auvipy]

+1

[carltongibson]

Do you think it's worth having a wrapper function that takes a version and a message...

 deprecated((3,1,3), "Moved to ... Use ... instead")

or such.

Inside we could check against the current version. Raise the appropriate warning. Assert False if too many versions have gone by.

If we used this everywhere we'd never miss any deprecations. We could also search for it to find all instances.

[xordoquy]

@carltongibson Really interesting.

[tomchristie]

Neat idea yeah.

[carltongibson]

OK. I'll draft something up.

(Put this in compat.py?)

[tomchristie]

Closing as per #3404. Don't see this as a priority, hasn't been a problem.