Fix: bad return and error naming

bitcask.go

@@ -77,7 +77,7 @@ func (db *DB) WithAll(action withAllAction) error {
 		case Sync:
 			err = namedErr(name, store.Sync())
 		default:
-			return unknownAction
+			return errUnknownAction
 		}
 		if err == nil {
 			continue

errors.go

@@ -5,13 +5,13 @@ import (
 	"strings"
 )
 
-var unknownAction = errors.New("unknown action")
+var errUnknownAction = errors.New("unknown action")
 
 func namedErr(name string, err error) error {
 	if err == nil {
 		return nil
 	}
-	errors.New(name+": "+err.Error())
+	return errors.New(name+": "+err.Error())
 }
 
 func compoundErrors(errs []error) error {