repo.gc - potentially insecure hash functions not allowed

#### Version information:
0.4.14

#### Type:
Bug

#### Description:

Low priority but I can't gc if I have a "insecure" hash:

```
$ ipfs repo gc
Error: "potentially insecure hash functions not allowed"
Please run 'ipfs pin verify' to list insecure hashes. If you want to read them, please downgrade your go-ipfs to 0.4.13
; garbage collection aborted: could not retrieve some links
```

```
$ ipfs pin verify
zDvnoLvmiom broken
zDvnoLvmiom: potentially insecure hash functions not allowed
```

Start by reproducing `ipfs repo gc` on the insecure hash shown by `ipfs pin verify`, using the reported version information as context. Trace how garbage collection retrieves links and handles the "potentially insecure hash functions not allowed" error; done should mean the intended garbage-collection behavior is verified by an appropriate regression test.

Written by the indexing model from the issue text.