wxGTK: incorrect wxSYS_COLOUR_HIGHLIGHT

[ATS]

> 
>  Hello,
> 
>  If I'm reading the code correctly, wxGTK doesn't interpret
> wxSYS_COLOUR_HIGHLIGHT correctly. This colour corresponds to Win32
> COLOR_HIGHLIGHT which is the colour of the background of an item selected
> (highlighted) in a control such as list box. The current code seems to be
> more appropriate for COLOR_3DHIGHLIGHT which is the colour which should be
> used for the faces of 3D objects facing the light source. For now I'll just
> make wxSYS_COLOUR_3DHILIGHT the same as wxSYS_COLOUR_HIGHLIGHT but the
> latter should really be changed to take its colours from a listbox and not
> a button IMO.
> 
>  Regards,
> VZ
> 

On GTK I also had problems with finding the "generic frame background colour"
(what is used for menubar, toolbar, panel and dialog background). 

The current implementation samples the colour from a dialog button. With
several GTK themes ("clearlooks"), this colour is lighter than the 
generic background colour. 

I made a patch improving on this: 

  [ 1887197 ] Menubar background colour

On Windows, wxSYS_COLOUR_BTNFACE always equals the generic panel colour. 
On GTK it is not so. 

Regards
// ATS.