fix(namesys) use the error that already exists

namesys/dns.go

 package namesys
 
 import (
-	"fmt"
 	"net"
 
 	b58 "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-base58"
@@ -9,8 +8,6 @@ import (
 	mh "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multihash"
 )
 
-var ErrNotFound = fmt.Errorf("namesys: name not found")
-
 // DNSResolver implements a Resolver on DNS domains
 type DNSResolver struct {
 	// TODO: maybe some sort of caching?
@@ -45,5 +42,5 @@ func (r *DNSResolver) Resolve(name string) (string, error) {
 		return t, nil
 	}
 
-	return "", ErrNotFound
+	return "", ErrResolveFailed
 }