Use the same "changed" GTK callback for wxComboBox and wxTextCtrl

And reuse EnableTextChangedEvents() between these classes as well.

No real changes so far, this is just a refactoring to centralize the
code in a single place before modifying it.

include/wx/gtk/textctrl.h

@@ -184,7 +184,6 @@ private:
     // overridden wxTextEntry virtual methods
     virtual GtkEditable *GetEditable() const wxOVERRIDE;
     virtual GtkEntry *GetEntry() const wxOVERRIDE;
-    virtual void EnableTextChangedEvents(bool enable) wxOVERRIDE;
 
     // change the font for everything in this control
     void ChangeFontGlobally();
@@ -198,7 +197,7 @@ private:
     // returns either m_text or m_buffer depending on whether the control is
     // single- or multi-line; convenient for the GTK+ functions which work with
     // both
-    void *GetTextObject() const
+    void *GetTextObject() const wxOVERRIDE
     {
         return IsMultiLine() ? static_cast<void *>(m_buffer)
                              : static_cast<void *>(m_text);