getHeads should do deduplication

[Powersource]

Here's my map

{
      '%QvMC8ErhfGpfThrxxpJ2M2FT5GJ8E5A74813Fe9MRCQ=.sha256': { '%YGUpnLZ5WF9QUcQyDv3qn8UImUK/mf1pf/ToqihLrSo=.sha256': 1 },
      '%YGUpnLZ5WF9QUcQyDv3qn8UImUK/mf1pf/ToqihLrSo=.sha256': {
        '%q05AUdw3PeWZ7bAMR2mxBKo6Ttz9DgvCukq9Nc73dxk=.sha256': 1,
        '%QaGyRlbX8s3pzmsWN0sqmMiJhUmuNXijTdUuhNPI5x0=.sha256': 1
      },
      '%QaGyRlbX8s3pzmsWN0sqmMiJhUmuNXijTdUuhNPI5x0=.sha256': { '%b/q1KPqRN45/5Kfakw7zz0TndBQGKZUpvYRAN4dVtGk=.sha256': 1 },
      '%q05AUdw3PeWZ7bAMR2mxBKo6Ttz9DgvCukq9Nc73dxk=.sha256': { '%b/q1KPqRN45/5Kfakw7zz0TndBQGKZUpvYRAN4dVtGk=.sha256': 1 }
    }

here's the output of getHeads

    [
      '%b/q1KPqRN45/5Kfakw7zz0TndBQGKZUpvYRAN4dVtGk=.sha256',
      '%b/q1KPqRN45/5Kfakw7zz0TndBQGKZUpvYRAN4dVtGk=.sha256'
    ]

I think users of the api probably expect keys to only occur once in the returned list.

[mixmix]

great catch! we should add a test around this case then have it pass. (it's been a while since I wrote that part of the code so I'd need tests to fix it well myself)

I'm honoured you've been reading and using this code so closely, and writing such great issues. Thanks @Powersource

[mixmix]

I think this is resolved now