exp/template: include function name in error returned by function or method call.

R=golang-dev, rsc, r
CC=golang-dev
https://golang.org/cl/4711049
diff --git a/src/pkg/exp/template/exec_test.go b/src/pkg/exp/template/exec_test.go
index 7e0301c8..112adbf 100644
--- a/src/pkg/exp/template/exec_test.go
+++ b/src/pkg/exp/template/exec_test.go
@@ -395,6 +395,9 @@
 	if err == nil {
 		t.Errorf("expected error; got none")
 	} else if !strings.Contains(err.String(), os.EPERM.String()) {
+		if *debug {
+			fmt.Printf("test execute error: %s\n", err)
+		}
 		t.Errorf("expected os.EPERM; got %s", err)
 	}
 }