Enable the use of context in restic

Set up a cancelble context in global options, hook it into the ctrl-C handler
for proper cancel propegation.

Bump up minimal requirement for Go to version 1.7 in documentation
and test-build files.

src/cmds/restic/global.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -33,6 +34,7 @@ type GlobalOptions struct {
 	NoLock       bool
 	JSON         bool
 
+	ctx      context.Context
 	password string
 	stdout   io.Writer
 	stderr   io.Writer
@@ -49,6 +51,13 @@ func init() {
 		globalOptions.password = pw
 	}
 
+	var cancel context.CancelFunc
+	globalOptions.ctx, cancel = context.WithCancel(context.Background())
+	AddCleanupHandler(func() error {
+		cancel()
+		return nil
+	})
+
 	f := cmdRoot.PersistentFlags()
 	f.StringVarP(&globalOptions.Repo, "repo", "r", os.Getenv("RESTIC_REPOSITORY"), "repository to backup to or restore from (default: $RESTIC_REPOSITORY)")
 	f.StringVarP(&globalOptions.PasswordFile, "password-file", "p", "", "read the repository password from a file")

src/cmds/restic/integration_helpers_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -194,6 +195,7 @@ func withTestEnvironment(t testing.TB, f func(*testEnvironment, GlobalOptions))
 	gopts := GlobalOptions{
 		Repo:     env.repo,
 		Quiet:    true,
+		ctx:      context.Background(),
 		password: TestPassword,
 		stdout:   os.Stdout,
 		stderr:   os.Stderr,