Ability to mark flags as deprecated

They will not show up in usage or help, but they will still work.
The usage message will print on os.Stderr any time the flag is set.

1 files changed, 2 insertions, 1 deletions

diff --git a/bool_test.go b/bool_test.go
index fe45b8d..2073590 100644
--- a/bool_test.go
+++ b/bool_test.go
@@ -156,7 +156,8 @@ func TestImplicitFalse(t *testing.T) {
 func TestInvalidValue(t *testing.T) {
 	var tristate triStateValue
 	f := setUpFlagSet(&tristate)
-	err := f.Parse([]string{"--tristate=invalid"})
+	args := []string{"--tristate=invalid"}
+	_, err := parseReturnStderr(t, f, args)
 	if err == nil {
 		t.Fatal("expected an error but did not get any, tristate has value", tristate)
 	}