fix(blockstore, bitswap) enforce threadsafety in blockstore

fixes data race detected in a testnet test
fix(bitswap) move mutex up to strategy from ledger

addresses concurrent access in bitswap session
Merge pull request #198 from jbenet/fix/bitswap-races

fix(bitswap) data races
rewrite findpeer and other dht tweaks
use my go-logging fork

until https://github.com/op/go-logging/pull/30 is merged
go-vet friendly codebase

- distinguish log.Error and log.Errorf functions
- Initialize structs with field names
- A bit of unreachable code (defers)