[ipfs/go-bitswap] Wantlist Race B

Forked from: https://github.com/ipfs/go-bitswap/issues/99

**Problem**

1. Peer A connects to peer B.
2. Peer A sends its wantlist to peer B.
3. Peer A disconnects from peer B.
4. Peer B notices the disconnect, forgets peer A's wantlist.
5. Peer A immediately reconnects to peer B.
6. Peer A notices the disconnect, sees that it still _has_ a connection, doesn't resend it's wantlist.

**Solution**

The only thing I can think of is the following: whenever the stream we're using to send wantlists closes, we (a) open a new one and (b) send the _complete_ wantlist. Unfortunately, I _really_ wanted to eventually move away from keeping a stream open entirely but, we'll, I can't think of a better solution.