hidden handles and get_children vs. get_all_children

[Kai Habel]

 Hello,

I think we need to replace in almost all places in graphics.cc and 
fltk_backend.cc the usage of get_children with get_all_children. 
Otherwise hidden handles are not considered. This is useful e.g. for 
generic menus to figure windows, which should be hidden from the user space.

I have attached a Changeset (w/o Changelog) to do the replacement, comments?

BTW, a hidden is only 'hidden' from the user space it is still visible.

Kai

Changeset.hidden_handles
Description: Text document