fix(exchange) add context to DialPeer
fix(net) pass contexts to dial peer
add do
fix(net) use Do to respect the caller's context
fix(do) child listens on ctx too
fix(bitswap) don't 'go' local function calls
fix(bitswap) always cancel on return
readability(util) Do -> ContextDo

@jbenet
Merge pull request #272 from jbenet/context-dial-peer

add context to DialPeer interface