Implement undo and redo for the ie and gtk webkit backends. Extend the sample to show their use.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68135 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/webview_ie.cpp

@@ -539,6 +539,25 @@ void wxWebViewIE::Paste()
     ExecCommand("Paste");
 }
 
+bool wxWebViewIE::CanUndo()
+{
+    return CanExecCommand("Undo");
+}
+bool wxWebViewIE::CanRedo()
+{
+    return CanExecCommand("Redo");
+}
+
+void wxWebViewIE::Undo()
+{
+    ExecCommand("Undo");
+}
+
+void wxWebViewIE::Redo()
+{
+    ExecCommand("Redo");
+}
+
 bool wxWebViewIE::CanExecCommand(wxString command)
 {
     wxVariant documentVariant = m_ie.GetProperty("Document");