If a model (1) defines a CounterField and (2) inherits from an

abstract model that defines a CounterField, then the magic that

CounterField does to replace _do_update on the model instance won't

work. It will call the equivalent of

super(type(model), model)._do_update, which, due to MRO, will resolve

to the method on the abstract model. However, that method has been

replaced by CounterField and it will have the same behaviour. Calling

super() this way only ever can take one step up the MRO chain (since

type(model) will never be the base class) and we therefore end up in a

loop of calling CounterField._do_update infinitely, which will blow

the stack.
We now reach directly to Model._do_update, avoiding the issues with

the MRO chain entirely, which results in the models being saved

successfully.
A unit test has been added (which, with this patch not applied, blows

the stack) to keep track of this edge case.

Ran unit tests.

Ran unit tests on /r/9609/ without blowing the stack.