Implement GetSelectedHTML for the ie and gtk webkit backends and document.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68226 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/webview_webkit.h

@@ -107,6 +107,7 @@ public:
     virtual bool HasSelection() { return false };
     virtual void SelectAll() {};
     virtual wxString GetSelectedText();
+    virtual wxString GetSelectedHTML() { return ""; }
 
     // ---- methods not from the parent (common) interface
     wxString RunScript(const wxString& javascript);