test: Make run.go's errorcheck behave like testlib.

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

test/run.go

@@ -522,7 +522,9 @@ func (t *test) errorCheck(outStr string, full, short string) (err error) {
 		}
 		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)
 		}
 	}
@@ -553,6 +555,13 @@ func (t *test) errorCheck(outStr string, full, short string) (err error) {
 		}
 	}
 
+	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
 	}