Improve behaviour of "force closing" wxDocuments

When the document was forced to close, OnSaveModified() was still called
and allowed the user to cancel closing the document -- but it was still
closed after OnSaveModified() returned.

Be more upfront about it and tell the user that the document will be
closed anyhow, but still propose them to save it if necessary.

An alternative solution might be to just deprecate "force closing"
entirely, as this seems very user-unfriendly.

samples/docview/docview.cpp

@@ -75,6 +75,7 @@ wxIMPLEMENT_APP(MyApp);
 
 wxBEGIN_EVENT_TABLE(MyApp, wxApp)
     EVT_MENU(wxID_ABOUT, MyApp::OnAbout)
+    EVT_MENU(wxID_CLEAR, MyApp::OnForceCloseAll)
 wxEND_EVENT_TABLE()
 
 MyApp::MyApp()
@@ -315,6 +316,7 @@ void MyApp::AppendDocumentFileCommands(wxMenu *menu, bool supportsPrinting)
     menu->Append(wxID_SAVE);
     menu->Append(wxID_SAVEAS);
     menu->Append(wxID_REVERT, _("Re&vert..."));
+    menu->Append(wxID_CLEAR, "&Force close all");
 
     if ( supportsPrinting )
     {
@@ -437,6 +439,13 @@ wxFrame *MyApp::CreateChildFrame(wxView *view, bool isCanvas)
     return subframe;
 }
 
+void MyApp::OnForceCloseAll(wxCommandEvent& WXUNUSED(event))
+{
+    // Pass "true" here to force closing just for testing this functionality,
+    // there is no real reason to force the issue here.
+    wxDocManager::GetDocumentManager()->CloseDocuments(true);
+}
+
 void MyApp::OnAbout(wxCommandEvent& WXUNUSED(event))
 {
     wxString modeName;

samples/docview/docview.h

@@ -71,6 +71,9 @@ private:
     void CreateMenuBarForFrame(wxFrame *frame, wxMenu *file, wxMenu *edit);
 
 
+    // force close all windows
+    void OnForceCloseAll(wxCommandEvent& event);
+
     // show the about box: as we can have different frames it's more
     // convenient, even if somewhat less usual, to handle this in the
     // application object itself