Allow selecting between primary and clipboard in text sample

Add a menu item to switch between using the clipboard and primary
selections.

This finally makes UsePrimarySelection() call in the sample useful,
after 25 years when it didn't do anything, since it was added back in
7e2c43b855 (...Added for primary selection to sample/text., 1999-06-10)

samples/text/text.cpp

@@ -410,6 +410,7 @@ enum
     TEXT_CLIPBOARD_COPY = 200,
     TEXT_CLIPBOARD_PASTE,
     TEXT_CLIPBOARD_VETO,
+    TEXT_CLIPBOARD_USE_PRIMARY,
 
     // tooltip menu
     TEXT_TOOLTIPS_SETDELAY = 300,
@@ -491,6 +492,10 @@ bool MyApp::OnInit()
     menuClipboard->Append(TEXT_CLIPBOARD_PASTE, "&Paste\tCtrl-Shift-V",
                           "Paste from clipboard to the text control");
     menuClipboard->AppendSeparator();
+    menuClipboard->AppendCheckItem(TEXT_CLIPBOARD_USE_PRIMARY,
+        "Use &primary selection\tCtrl-Shift-P",
+        "If checked, use primary selection instead of clipboard");
+    menuClipboard->AppendSeparator();
     menuClipboard->AppendCheckItem(TEXT_CLIPBOARD_VETO, "Vet&o\tCtrl-Shift-O",
                                    "Veto all clipboard operations");
     menu_bar->Append(menuClipboard, "&Clipboard");
@@ -1315,9 +1320,11 @@ wxTextCtrl *MyPanel::GetFocusedText() const
 #if wxUSE_CLIPBOARD
 void MyPanel::SelectClipboardSelection()
 {
-    // On X11, we want to exchange data with the clipboard selection instead
-    // of the primary selection -- which is actually the case by default.
-    wxTheClipboard->UsePrimarySelection(false);
+    wxFrame *frame = wxDynamicCast(wxGetTopLevelParent(this), wxFrame);
+    wxCHECK_RET( frame, "no parent frame?" );
+
+    wxTheClipboard->UsePrimarySelection(
+        frame->GetMenuBar()->IsChecked(TEXT_CLIPBOARD_USE_PRIMARY));
 }
 
 void MyPanel::DoPasteFromClipboard()