Add wxRichMessageDialog class.

This is a generalization of wxMessageDialog based on the native task dialog
under recent (Vista and later) Windows versions and implemented generically
for the other ports for now.

It provides the possibility to use additional controls in the message boxes
(checkbox useful for the "Don't ask me again" kind of dialogs and collapsible
detailed explanations field) and better look and feel under Windows.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65349 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/os2/setup0.h

@@ -751,6 +751,7 @@
 #define wxUSE_LISTCTRL      1   // wxListCtrl
 #define wxUSE_RADIOBOX      1   // wxRadioBox
 #define wxUSE_RADIOBTN      1   // wxRadioButton
+#define wxUSE_RICHMSGDLG    1   // wxRichMessageDialog
 #define wxUSE_SCROLLBAR     1   // wxScrollBar
 #define wxUSE_SEARCHCTRL    1   // wxSearchCtrl
 #define wxUSE_SLIDER        1   // wxSlider