Only ignore Alt down on Mac

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@56014 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/richtext/richtextctrl.cpp

@@ -983,7 +983,11 @@ void wxRichTextCtrl::OnChar(wxKeyEvent& event)
 
             default:
             {
+#ifdef __WXMAC__
                 if (event.CmdDown())
+#else
+                if (event.CmdDown() || event.AltDown())
+#endif
                 {
                     event.Skip();
                     return;