feat(bitswap) find providers for all keys on wantlist

@jbenet @whyrusleeping

this addresses a failure case where

1) bitswap wants blocks A and B
2) partner 1 has A and partner 2 has B
3) We choose a key at random, drawing A.
4) Then, we request A, neglecting to find a provider for B.

Sending the full wantlist is meant to be used as a helpful additional
piece of data, but...

unless our hunch is support by statistical inference at runtime,
it's not safe to assume that a peer will have blocks for related keys.
Routing must be the source of truth.

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>

bitswap.go

@@ -3,7 +3,6 @@
 package bitswap
 
 import (
-	"math/rand"
 	"time"
 
 	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
@@ -175,17 +174,13 @@ func (bs *bitswap) run(ctx context.Context) {
 	for {
 		select {
 		case <-broadcastSignal.C:
-			wantlist := bs.wantlist.Keys()
-			if len(wantlist) == 0 {
-				continue
-			}
-			n := rand.Intn(len(wantlist))
-			providers := bs.routing.FindProvidersAsync(ctx, wantlist[n], maxProvidersPerRequest)
-
+			for _, k := range bs.wantlist.Keys() {
+				providers := bs.routing.FindProvidersAsync(ctx, k, maxProvidersPerRequest)
 				err := bs.sendWantListTo(ctx, providers)
 				if err != nil {
 					log.Errorf("error sending wantlist: %s", err)
 				}
+			}
 		case ks := <-bs.batchRequests:
 			// TODO: implement batching on len(ks) > X for some X
 			if len(ks) == 0 {