PVP proposal: don't require major version bump when adding non-orphan instances

[Yitzchak Gale]

Johan Tibell wrote:
> we could change the first two PVP rules to...
> ...or _orphan_ instances were added or
> _any_ instances were removed...
> I believe this would result in less work for maintainers.

The burden is actually not nearly as onerous as it used
to be with the many great new Cabal features that allow
manually tweaking cabal's build plan in various ways.
Many thanks to Johan and the Cabal team!

But yes, I agree, this is a good change to PVP.
+1

Christian Maeder wrote:
>> I tend to agree to this proposal, but I would like to encourage
>> developers/researchers to invent something like named instances (or
>> dictionaries), that are not transitively reexported and could coexist
>> with current instances. (These would allow several, differently named,
>> instances for the same type and class combination.)

Henning Thielemann wrote:
> ...What about packing and unpacking of
> class dictionaries in existentially quantified types?

I strongly agree with Christian, and I thank Henning
for suggesting an implementation direction.

But - focus, focus, focus! Make believe I never said
that.

Thanks,
Yitz