Determine the enabled state using IsThisEnabled() instead of
IsEnabled(), because the latter returns false if the entire window is
disabled without its appearance being affected, e.g. if another window
is shown modally.
This is a simple animated control indicating some program activity.
Provide native GTK+ (for > 2.20) and OS X implementations as well as a generic
one used under MSW.
Update the sample and the documentation.