refactor(routing) replace u.ErrNotFound with routing.ErrNotFound

fix(bitswap/message) duplicate entries

to emphasize idempotence

comes at the cost of O(n) Blocks() method.

so there's one less name to think about

A nice invariant for bitswap sessions:

        Senders and receivers can trust that messages do not contain
        duplicate blocks or duplicate keys. Backing the message with a
        map enforces this invariant.

        This comes at the cost of O(n) getters.

implementation will be patched to ensure bitswap messages cannot contain
duplicate blocks or keys

@whyrusleeping noticed this a couple days ago

potential long-term fix: prevent duplicate entries in the wantlist by
using a map/set and iterating over this data structure on export

Revert "perf(mux) use RWMutex"

perf(mux) use RWMutex

ipfs tour

Improve tests

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>

- if equinox says there is a new update, but the version number IS NOT
larger, we interpret that as no update (you may have gotten a newer
version by building it yourself).

- Also export ErrNoUpdateAvailable so clients don't also need to
import the equinox library to check the error.

cc @cryptix comments?

ContextCloserify

- less floating variables

convert DAGService to an interface

Fix logs + msgio error