Support CIDs in dag-pb links

[olizilla]

js-ipld-dag-pb assumes that links will be multihashes

js-ipld-dag-pb/src/dag-link/index.js

Lines 8 to 23 in 70b0cd5

	class DAGLink {
	constructor (name, size, multihash) {
	assert(multihash, 'A link requires a multihash to point to')
	// assert(size, 'A link requires a size')
	// note - links should include size, but this assert is disabled
	// for now to maintain consistency with go-ipfs pinset
	this._name = name || ''
	this._size = size
	if (typeof multihash === 'string') {
	this._multihash = mh.fromB58String(multihash)
	} else if (Buffer.isBuffer(multihash)) {
	this._multihash = multihash
	}
	}

Here is a dag-pb node where one of the links is a CIDv1
https://ipfs.io/api/v0/dag/get?arg=QmViWi5az9iiPzESM6ruHf84TcmHSAVQ2KQdNveoDH7eaY/refs/heads

// 20180731162407
// https://ipfs.io/api/v0/dag/get?arg=QmViWi5az9iiPzESM6ruHf84TcmHSAVQ2KQdNveoDH7eaY/refs/heads

{
  "data": "CAE=",
  "links": [
    {
      "Name": "archive",
      "Size": 83,
      "Cid": {
        "/": "QmfBgo8BAB26hFtyGNGK46rqYkKLFvWYfTqjrGdbUEjnUU"
      }
    },
    {
      "Name": "master",
      "Size": 42,
      "Cid": {
        "/": "z8mWaJHXieAVxxLagBpdaNWFEBKVWmMiE"
      }
    }
  ]
}

I assume we need to upgrade DagLink to support CIDs, but I've never seen one like that before, so I first want to verify that such a thing should be possible.

[vmx]

@diasdavid, @Stebalien Can you help?

[Stebalien]

Yes, they can be CIDv1 links. Specifically, unixfs can store CIDv1 pointers to raw blocks. That's how we implement the raw leaves feature (where we store file chunks as raw data instead of wrapping them in protobufs).