Add basic history api and implement it under gtk.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68108 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/webview_ie.h

@@ -50,6 +50,8 @@ public:
     virtual bool CanGoBack() { return m_canNavigateBack; }
     virtual void GoBack();
     virtual void GoForward();
+    virtual void ClearHistory() {};
+    virtual void EnableHistory(bool enable = true) {};
     virtual void Stop();
     virtual void Reload(wxWebViewReloadFlags flags = wxWEB_VIEW_RELOAD_DEFAULT);