serve restic: disallow on go1.8 because of dependent library changes

golang.org/x/net/http2 no longer builds on go1.8

cmd/serve/restic/restic.go

@@ -1,4 +1,7 @@
 // Package restic serves a remote suitable for use with restic
+
+// +build go1.9
+
 package restic
 
 import (

cmd/serve/restic/restic_appendonly_test.go

@@ -1,3 +1,5 @@
+// +build go1.9
+
 package restic
 
 import (

cmd/serve/restic/restic_test.go

@@ -1,5 +1,8 @@
 // Serve restic tests set up a server and run the integration tests
 // for restic against it.
+
+// +build go1.9
+
 package restic
 
 import (

cmd/serve/restic/restic_unsupported.go

@@ -0,0 +1,11 @@
+// Build for unsupported platforms to stop go complaining
+// about "no buildable Go source files "
+
+// +build !go1.9
+
+package restic
+
+import "github.com/spf13/cobra"
+
+// Command definition is nil to show not implemented
+var Command *cobra.Command = nil

cmd/serve/restic/stdio_conn.go

@@ -1,3 +1,5 @@
+// +build go1.9
+
 package restic
 
 import (

cmd/serve/restic/stdio_conn_pre_go1.10.go

@@ -1,4 +1,4 @@
-//+build !go1.10
+//+build go1.9,!go1.10
 
 // Fallback deadline setting for pre go1.10
 

cmd/serve/serve.go

@@ -16,7 +16,9 @@ func init() {
 	if webdav.Command != nil {
 		Command.AddCommand(webdav.Command)
 	}
-	Command.AddCommand(restic.Command)
+	if restic.Command != nil {
+		Command.AddCommand(restic.Command)
+	}
 	if ftp.Command != nil {
 		Command.AddCommand(ftp.Command)
 	}