Move multierror logic into luci-go.

common/errors/markederror.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package errors
 
 import (
+        "errors"
         "fmt"
         "path/filepath"
         "runtime"
 )
 
+// New is a pass-through version of the standard errors.New function.
+var New = errors.New
+
 // MarkedError is the specific error type retuned by MakeMarkFn. It's designed
 // so that you can access the underlying object if needed.
 type MarkedError struct {
         // Orig contains the original data (error or otherwise) which was passed to
         // the marker function.
         Orig interface{}
 
         msgFmt string
 }
 
@@ skipping 12 matching lines @@
                         return nil
                 }
                 _, filename, line, gotInfo := runtime.Caller(1)
                 pfx := fmtstring2
                 if gotInfo {
                         pfx = fmt.Sprintf(fmtstring1, filepath.Base(filename), line)
                 }
                 return &MarkedError{errish, pfx}
         }
 }