added (MSW/GTK) and documented new frame and dialog flags

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@8523 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk1/dialog.cpp

@@ -632,7 +632,9 @@ int wxDialog::ShowModal()
        return GetReturnCode();
     }
 
-    if ( !GetParent() )
+    // use the apps top level window as parent if none given unless explicitly
+    // forbidden
+    if ( !GetParent() && !(GetWindowStyleFlag() & wxDIALOG_NO_PARENT) )
     {
         wxWindow *parent = wxTheApp->GetTopWindow();
         if ( parent && parent != this )