openpgp: fix error strings and typos.

Fixes golang/go#2841.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5688054

openpgp/packet/config.go

@@ -12,8 +12,7 @@ import (
 )
 
 // Config collects a number of parameters along with sensible defaults.
-
-// A nil *Config is valid and produces all default values.
+// A nil *Config is valid and results in all default values.
 type Config struct {
 	// Rand provides the source of entropy.
 	// If nil, the crypto/rand Reader is used.

openpgp/packet/signature.go

@@ -483,13 +483,14 @@ func (sig *Signature) SignKey(pub *PublicKey, priv *PrivateKey, config *Config)
 	return sig.Sign(h, priv, config)
 }
 
-// Serialize marshals sig to w. SignRSA or SignDSA must have been called first.
+// Serialize marshals sig to w. Sign, SignUserId or SignKey must have been
+// called first.
 func (sig *Signature) Serialize(w io.Writer) (err error) {
 	if len(sig.outSubpackets) == 0 {
 		sig.outSubpackets = sig.rawSubpackets
 	}
 	if sig.RSASignature.bytes == nil && sig.DSASigR.bytes == nil {
-		return errors.InvalidArgumentError("Signature: need to call SignRSA or SignDSA before Serialize")
+		return errors.InvalidArgumentError("Signature: need to call Sign, SignUserId or SignKey before Serialize")
 	}
 
 	sigLength := 0