Add wxPreferencesEditor::ShownModally().

While this is not necessary to use wxPreferencesEditor in normal scenario, it
can be useful if the program needs to handle modal dialogs in some special way.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74009 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/preferences.h

@@ -98,6 +98,23 @@ public:
         in this case as well.
      */
     static bool ShouldApplyChangesImmediately()
+
+    /**
+        Returns whether the preferences dialog is shown modally.
+
+        If this method returns false, as it currently does in wxGTK and wxOSX,
+        Show() simply makes the dialog visible and returns immediately. If it
+        returns true, as it does in wxMSW and under the other platforms, then
+        the dialog is shown modally, i.e. Show() blocks until the user
+        dismisses it.
+
+        Notice that it isn't necessary to test the return value of this method
+        to use this class normally, its interface is designed to work in both
+        cases. However it can sometimes be necessary to call it if the program
+        needs to handle modal dialogs specially, e.g. perhaps to block some
+        periodic background update operation while a modal dialog is shown.
+     */
+    static bool ShownModally();
 };