Fix backup test and doc.

backup.go

@@ -22,8 +22,10 @@ import (
 //	// check err
 //	cbs := make(chan sqlite.BackupStatus)
 //	go func() {
-//		s := <- cbs
-//		// report progress
+//		for {
+//			s := <- cbs
+//			// report progress
+//		}
 //	}()
 //	err = bck.Run(100, 250000, cbs)
 //	check(err)

backup_test.go

@@ -17,9 +17,11 @@ func TestBackup(t *testing.T) {
 
 	cbs := make(chan BackupStatus)
 	go func() {
-		s := <- cbs
-		t.Logf("Backup progress %#v\n", s)
+		for {
+			s := <- cbs
+			t.Logf("Backup progress %#v\n", s)
+		}
 	}()
-	err = bck.Run(100, 0, cbs)
+	err = bck.Run(10, 0, cbs)
 	checkNoError(t, err, "couldn't do backup: %#v")
 }
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