address comments from PR

blocks.go

 package blocks
 
 import (
+	"errors"
 	"fmt"
 
 	mh "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multihash"
@@ -18,6 +19,16 @@ func NewBlock(data []byte) *Block {
 	return &Block{Data: data, Multihash: u.Hash(data)}
 }
 
+func NewBlockWithHash(data []byte, h mh.Multihash) (*Block, error) {
+	if u.Debug {
+		chk := u.Hash(data)
+		if string(chk) != string(h) {
+			return nil, errors.New("Data did not match given hash!")
+		}
+	}
+	return &Block{Data: data, Multihash: h}, nil
+}
+
 // Key returns the block's Multihash as a Key value.
 func (b *Block) Key() u.Key {
 	return u.Key(b.Multihash)