Add RunScript and implement on all backends. Document and add a very simple unit test.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68275 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/webview_webkit.h

@@ -149,6 +149,8 @@ public:
     virtual wxString GetSelectedSource();
     virtual void ClearSelection();
 
+    virtual void RunScript(const wxString& javascript);
+
     /** FIXME: hack to work around signals being received too early */
     bool m_ready;