crypto/x509: harmonise error prefixes.

crypto/x509 has ended up with a variety of error formats. This change makes them all start with "x509: ".

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/9736043
diff --git a/src/pkg/crypto/x509/pkcs1.go b/src/pkg/crypto/x509/pkcs1.go
index 873d396..acebe35 100644
--- a/src/pkg/crypto/x509/pkcs1.go
+++ b/src/pkg/crypto/x509/pkcs1.go
@@ -52,7 +52,7 @@
 	}
 
 	if priv.N.Sign() <= 0 || priv.D.Sign() <= 0 || priv.P.Sign() <= 0 || priv.Q.Sign() <= 0 {
-		return nil, errors.New("private key contains zero or negative value")
+		return nil, errors.New("x509: private key contains zero or negative value")
 	}
 
 	key = new(rsa.PrivateKey)
@@ -67,7 +67,7 @@
 	key.Primes[1] = priv.Q
 	for i, a := range priv.AdditionalPrimes {
 		if a.Prime.Sign() <= 0 {
-			return nil, errors.New("private key contains zero or negative prime")
+			return nil, errors.New("x509: private key contains zero or negative prime")
 		}
 		key.Primes[i+2] = a.Prime
 		// We ignore the other two values because rsa will calculate
diff --git a/src/pkg/crypto/x509/pkcs8.go b/src/pkg/crypto/x509/pkcs8.go
index 8e1585e..ba19989 100644
--- a/src/pkg/crypto/x509/pkcs8.go
+++ b/src/pkg/crypto/x509/pkcs8.go
@@ -32,7 +32,7 @@
 	case privKey.Algo.Algorithm.Equal(oidPublicKeyRSA):
 		key, err = ParsePKCS1PrivateKey(privKey.PrivateKey)
 		if err != nil {
-			return nil, errors.New("crypto/x509: failed to parse RSA private key embedded in PKCS#8: " + err.Error())
+			return nil, errors.New("x509: failed to parse RSA private key embedded in PKCS#8: " + err.Error())
 		}
 		return key, nil
 
@@ -44,11 +44,11 @@
 		}
 		key, err = parseECPrivateKey(namedCurveOID, privKey.PrivateKey)
 		if err != nil {
-			return nil, errors.New("crypto/x509: failed to parse EC private key embedded in PKCS#8: " + err.Error())
+			return nil, errors.New("x509: failed to parse EC private key embedded in PKCS#8: " + err.Error())
 		}
 		return key, nil
 
 	default:
-		return nil, fmt.Errorf("crypto/x509: PKCS#8 wrapping contained private key with unknown algorithm: %v", privKey.Algo.Algorithm)
+		return nil, fmt.Errorf("x509: PKCS#8 wrapping contained private key with unknown algorithm: %v", privKey.Algo.Algorithm)
 	}
 }
diff --git a/src/pkg/crypto/x509/sec1.go b/src/pkg/crypto/x509/sec1.go
index 8a2840f..3a0e29a 100644
--- a/src/pkg/crypto/x509/sec1.go
+++ b/src/pkg/crypto/x509/sec1.go
@@ -40,10 +40,10 @@
 func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *ecdsa.PrivateKey, err error) {
 	var privKey ecPrivateKey
 	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
-		return nil, errors.New("crypto/x509: failed to parse EC private key: " + err.Error())
+		return nil, errors.New("x509: failed to parse EC private key: " + err.Error())
 	}
 	if privKey.Version != ecPrivKeyVersion {
-		return nil, fmt.Errorf("crypto/x509: unknown EC private key version %d", privKey.Version)
+		return nil, fmt.Errorf("x509: unknown EC private key version %d", privKey.Version)
 	}
 
 	var curve elliptic.Curve
@@ -53,12 +53,12 @@
 		curve = namedCurveFromOID(privKey.NamedCurveOID)
 	}
 	if curve == nil {
-		return nil, errors.New("crypto/x509: unknown elliptic curve")
+		return nil, errors.New("x509: unknown elliptic curve")
 	}
 
 	k := new(big.Int).SetBytes(privKey.PrivateKey)
 	if k.Cmp(curve.Params().N) >= 0 {
-		return nil, errors.New("crypto/x509: invalid elliptic curve private key value")
+		return nil, errors.New("x509: invalid elliptic curve private key value")
 	}
 	priv := new(ecdsa.PrivateKey)
 	priv.Curve = curve
diff --git a/src/pkg/crypto/x509/x509.go b/src/pkg/crypto/x509/x509.go
index 4dfea2c..d789e5c 100644
--- a/src/pkg/crypto/x509/x509.go
+++ b/src/pkg/crypto/x509/x509.go
@@ -40,7 +40,7 @@
 	}
 	algo := getPublicKeyAlgorithmFromOID(pki.Algorithm.Algorithm)
 	if algo == UnknownPublicKeyAlgorithm {
-		return nil, errors.New("ParsePKIXPublicKey: unknown public key algorithm")
+		return nil, errors.New("x509: unknown public key algorithm")
 	}
 	return parsePublicKey(algo, &pki)
 }
@@ -56,7 +56,7 @@
 			E: pub.E,
 		})
 	default:
-		return nil, errors.New("MarshalPKIXPublicKey: unknown public key type")
+		return nil, errors.New("x509: unknown public key type")
 	}
 
 	pkix := pkixPublicKey{
@@ -477,7 +477,7 @@
 
 // ErrUnsupportedAlgorithm results from attempting to perform an operation that
 // involves algorithms that are not currently implemented.
-var ErrUnsupportedAlgorithm = errors.New("crypto/x509: cannot verify signature: algorithm unimplemented")
+var ErrUnsupportedAlgorithm = errors.New("x509: cannot verify signature: algorithm unimplemented")
 
 // ConstraintViolationError results when a requested usage is not permitted by
 // a certificate. For example: checking a signature when the public key isn't a
@@ -485,7 +485,7 @@
 type ConstraintViolationError struct{}
 
 func (ConstraintViolationError) Error() string {
-	return "crypto/x509: invalid signature: parent certificate cannot sign this kind of certificate"
+	return "x509: invalid signature: parent certificate cannot sign this kind of certificate"
 }
 
 func (c *Certificate) Equal(other *Certificate) bool {
@@ -604,10 +604,10 @@
 			return err
 		}
 		if dsaSig.R.Sign() <= 0 || dsaSig.S.Sign() <= 0 {
-			return errors.New("DSA signature contained zero or negative values")
+			return errors.New("x509: DSA signature contained zero or negative values")
 		}
 		if !dsa.Verify(pub, digest, dsaSig.R, dsaSig.S) {
-			return errors.New("DSA verification failure")
+			return errors.New("x509: DSA verification failure")
 		}
 		return
 	case *ecdsa.PublicKey:
@@ -616,10 +616,10 @@
 			return err
 		}
 		if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
-			return errors.New("crypto/x509: ECDSA signature contained zero or negative values")
+			return errors.New("x509: ECDSA signature contained zero or negative values")
 		}
 		if !ecdsa.Verify(pub, digest, ecdsaSig.R, ecdsaSig.S) {
-			return errors.New("crypto/x509: ECDSA verification failure")
+			return errors.New("x509: ECDSA verification failure")
 		}
 		return
 	}
@@ -635,7 +635,7 @@
 type UnhandledCriticalExtension struct{}
 
 func (h UnhandledCriticalExtension) Error() string {
-	return "unhandled critical extension"
+	return "x509: unhandled critical extension"
 }
 
 type basicConstraints struct {
@@ -694,7 +694,7 @@
 			return nil, err
 		}
 		if p.Sign() <= 0 || params.P.Sign() <= 0 || params.Q.Sign() <= 0 || params.G.Sign() <= 0 {
-			return nil, errors.New("zero or negative DSA parameter")
+			return nil, errors.New("x509: zero or negative DSA parameter")
 		}
 		pub := &dsa.PublicKey{
 			Parameters: dsa.Parameters{
@@ -714,11 +714,11 @@
 		}
 		namedCurve := namedCurveFromOID(*namedCurveOID)
 		if namedCurve == nil {
-			return nil, errors.New("crypto/x509: unsupported elliptic curve")
+			return nil, errors.New("x509: unsupported elliptic curve")
 		}
 		x, y := elliptic.Unmarshal(namedCurve, asn1Data)
 		if x == nil {
-			return nil, errors.New("crypto/x509: failed to unmarshal elliptic curve point")
+			return nil, errors.New("x509: failed to unmarshal elliptic curve point")
 		}
 		pub := &ecdsa.PublicKey{
 			Curve: namedCurve,
@@ -752,7 +752,7 @@
 	}
 
 	if in.TBSCertificate.SerialNumber.Sign() < 0 {
-		return nil, errors.New("negative serial number")
+		return nil, errors.New("x509: negative serial number")
 	}
 
 	out.Version = in.TBSCertificate.Version + 1