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Let's save log.Error for things the user can take action on.
Moved all our diagnostics to log.Debug. We can ideally reduce them
even further.

this will help us introspect what's going on.

This addr manager should seriously help with the addrsplosion
problem.

unixfs file size != merkledag cumulative size

⚠ this commit makes your current configs unusable, as the
default bootstrap peers. You may need to edit your config.

Go from:

```js
Bootstrap: [
  {
    "Address": "/ip4/104.131.131.82/tcp/4001",
    "PeerID": "QmaCpDMGvV2BGHeYERUEnRQAwe3N8SzbUtfsmvsqQLuvuJ"
  }
]
```

To:
```js
Bootstrap: [
  "/ip4/104.131.131.82/tcp/4001/ipfs/QmaCpDMGvV2BGHeYERUEnRQAwe3N8SzbUtfsmvsqQLuvuJ"
]
```

Addresses bug #689

This commit removes the dependency on go-fuse-version, and thus the
fuse headers. It also introduces an elaborate troubleshooting process
that diagnoses whether fuse installed -- and which version -- with as
little requirements as possible (attept to use sysctl, fall-back on
the go-fuse-version binary, etc). It then nicely instructs the user
what to do next.