[TRY 3] Add support for tooltips for system tray icons

[James Liggett]

Hi Kuba,
> 
> What about a static variable right in the function where you call the 
> initialization function? That'd work fine if you don't call 
> InitCommonControlsEx from anywhere else:
> 
> if (!list_head(&tray.icons))
> {
> 	static BOOL controls_initialized = FALSE;
> 	INITCOMMONCONTROLSEX init_tooltip;
> 
> 	init_tooltip.dwSize = sizeof(INITCOMMONCONTROLSEX);
> 	init_tooltip.dwICC = ICC_TAB_CLASSES;
> 
> 	if (! controls_initialized) {
> 		InitCommonControlsEx(&init_tooltip);
> 		controls_initialized = TRUE;
> 	}
> 	. . .
> }
Indeed, that's what I ended up doing. Mike committed it to his temporary
git tree.