misc(crypto) remove stale test

@jbenet

Handshake library has been modified to use Secure Pipe. This test
targets the old implementation.

TODO: write a new handshake test
style(bitswap) make signature more readable
chore(bitswap) cleanup
style(bitswap) swap argument order
fix(exch) name the error
test(bitswap) test sending wantlist to peers
fix(bitswap:testnet) Provide takes ctx
fix(bitswap) keep interface the same

changing the bitswap interace breaks tests and makes things a bit
difficult going forward. I think I have a temporary solution to replace
the async method.

this commit partially reverts changes from:

ec50703395098f75946f0bad01816cc54ab18a58

https://github.com/jbenet/go-ipfs/commit/ec50703395098f75946f0bad01816cc54ab18a58
fix(routing:dht) implement FindProvidersAsync in terms of FindProviders

until construction is complete on the actual async method

reverts changes from ec50703395098f75946f0bad01816cc54ab18a58

https://github.com/jbenet/go-ipfs/commit/ec50703395098f75946f0bad01816cc54ab18a58
test(bitswap) send entire wantlist to peers

fix(bitswap) pass go vet

fixes #97

https://github.com/jbenet/go-ipfs/issues/97
refac(bitswap, util) extract KeySet
feat(bitswap) expose ability to toggle "niceness"

true -> always send to peer

false -> use ledger-based strategy described in IPFS paper draft 3
doc(bitswap:strat) add note to remove blocks from peer's wantlist after
sending