[release/1.4.11] eth, eth/downloader: don't forward the DAO challenge header

(cherry picked from commit 071af57)

Author: karalabe

eth/downloader/downloader.go

@@ -542,7 +542,7 @@ func (d *Downloader) fetchHeight(p *peer) (*types.Header, error) {
 // In the rare scenario when we ended up on a long reorganisation (i.e. none of
 // the head links match), we do a binary search to find the common ancestor.
 func (d *Downloader) findAncestor(p *peer, height uint64) (uint64, error) {
-	glog.V(logger.Debug).Infof("%v: looking for common ancestor", p)
+	glog.V(logger.Debug).Infof("%v: looking for common ancestor (remote height %d)", p, height)
 
 	// Figure out the valid ancestor range to prevent rewrite attacks
 	floor, ceil := int64(-1), d.headHeader().Number.Uint64()

eth/handler.go

@@ -434,6 +434,7 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 					return err
 				}
 				glog.V(logger.Debug).Infof("%v: verified to be on the same side of the DAO fork", p)
+				return nil
 			}
 			// Irrelevant of the fork checks, send the header to the fetcher just in case
 			headers = pm.fetcher.FilterHeaders(headers, time.Now())