Instead we have an alternate code path for the appropriate API entry
points in uxtheme.dll.
This is not the best organizational structure. We should probably have
HTHEME handles resolve to an object with its own function table, so
then we have an MSSTYLES backend and a GTK backend and what have
you. It would also be better to avoid having GTK controlled with its
own registry key like this but rather to have it be selectable using
EnumThemes()/ApplyTheme() [presumably through a fake theme file, as
was used in the original implementation], so that we don't have to
have special handling for those functions and everything can just be
part of the HTHEME backend. However, time is currently of the essence,
and this will have to do for the moment.
