Add Go 1.4 compatibility layer for raw64

Using raw64 will not work, but at least it will compile.

internal/nametransform/names.go

@@ -25,7 +25,7 @@ type NameTransform struct {
 func New(c *cryptocore.CryptoCore, longNames bool, raw64 bool) *NameTransform {
 	b64 := base64.URLEncoding
 	if raw64 {
-		b64 = base64.RawURLEncoding
+		b64 = getRaw64Encoding()
 	}
 	return &NameTransform{
 		cryptoCore: c,

internal/nametransform/raw64_go1.4.go

@@ -0,0 +1,18 @@
+//+build !go1.5
+
+package nametransform
+
+import (
+	"encoding/base64"
+	"log"
+)
+
+const (
+	HaveRaw64 = false
+)
+
+func getRaw64Encoding() *base64.Encoding {
+	log.Panicf("Tried to use base64.RawURLEncoding but your Go version does not provide it.\n" +
+		"You need Go 1.5 or higher.")
+	return nil
+}

internal/nametransform/raw64_go1.5.go

@@ -0,0 +1,15 @@
+//+build go1.5
+
+package nametransform
+
+import (
+	"encoding/base64"
+)
+
+const (
+	HaveRaw64 = true
+)
+
+func getRaw64Encoding() *base64.Encoding {
+	return base64.RawURLEncoding
+}

tests/matrix/matrix_test.go

@@ -24,6 +24,7 @@ import (
 	"testing"
 
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/tests/test_helpers"
 )
@@ -63,6 +64,10 @@ func TestMain(m *testing.M) {
 			fmt.Printf("Skipping Go GCM variant, Go installation is too old")
 			continue
 		}
+		if testcase.raw64 && !nametransform.HaveRaw64 {
+			fmt.Printf("Skipping raw64 test, Go installation is too old")
+			continue
+		}
 		if testing.Verbose() {
 			fmt.Printf("matrix: testcase = %#v\n", testcase)
 		}