testlib will complain about any unmatched errors left in errorchecks while run.go will not.
Fixes #4141.
R=golang-dev, minux.ma, remyoudompheng, rsc
CC=golang-dev
https://golang.org/cl/
6614060
                }
                if strings.HasPrefix(line, "\t") {
                        out[len(out)-1] += "\n" + line
-               } else {
+               } else if strings.HasPrefix(line, "go tool") {
+                       continue
+               } else if strings.TrimSpace(line) != "" {
                        out = append(out, line)
                }
        }
                }
        }
 
+       if len(out) > 0 {
+               errs = append(errs, fmt.Errorf("Unmatched Errors:"))
+               for _, errLine := range out {
+                       errs = append(errs, fmt.Errorf("%s", errLine))
+               }
+       }
+
        if len(errs) == 0 {
                return nil
        }