Program Repair Shop

`Global variables`

%P, the cache of @ISA information, doesn't bother me so much
It is not truly global
It's just a cache
- Such caches are typically used by only one function
- In this case, _obs_get_parent_observers
So I would have preferred to see something like:

        { my %P;    # Cache
          sub _obs_get_parent_observers {
            ...
          }
        }