/ipfs/ and /ipns/ links don't work from a dnslink hosted web space

#### Version information:
go-ipfs version: 0.4.9-rc1-
Repo version: 5
System version: amd64/darwin
Golang version: go1.8

#### Type: Bug

#### Severity: Medium

#### Description:

When accessing IPFS via a dnslink-serviced host (e.g. ipfs.sallings.org), `/ipfs/` and `/ipns/` links don't work.

e.g.,:

http://ipfs.sallings.org/ipns/QmP8uqUuowHdixyFASba87ABgVxfoKGj8NyrTH2VLLTFkZ

yields:

ipfs resolve -r /ipns/ipfs.sallings.org/ipns/QmP8uqUuowHdixyFASba87ABgVxfoKGj8NyrTH2VLLTFkZ: no link named "ipns" under QmaYYjrg1rEYddWYLcR96uc9jGLA9cuHkUiCqQYLwbKDnx

I would expect either `ipfs` or `ipns` to be handled in this case when it can't be resolved directly (or just always).

This seems minor, but I considered it "medium" severity as it means you can't link to separately managed pages within IPFS from such a host. In the above case, I worked around this by linking to `//gateway.ipfs.io/ipns/...` -- but this is quite undesirable for a variety of reasons (e.g., can't just browse stuff at localhost).