PeerApi: Prove a method to "sync" with the currently-connected peers

[kim]

This would require protocol support for efficiently computing the intersection of URNs two peers have locally. As a first step, however, we can just implement it as a loop which calls Storage::fetch_repo for each local URN and connected peer, ignoring errors.

[FintanH]

So interestingly enough @xla pretty much implemented this in proxy. This is likely one of the components that we should migrate back to link.

[kim]

Yes would be good, so we can replace it with a more efficient implementation.

[xla]

Yes would be good, so we can replace it with a more efficient implementation.

:100: